The versatility of proteins: from biomolecules to biopharmaceuticals
Ambika C. Banerjee
East India Pharmaceutical Works Ltd., 6, Little Russell Street,
Kolkata- 700 071, India.
Corresponding author:
Ambika C. Banerjee, Corporate Advisor, Research & Development,
East India Pharmaceutical Works Ltd., 6, Little Russell Street, Kolkata-
700 071, India.
E-mail: banerjeeac@yahoo.in, Tel: +919831175103
ABSTRACT
The vast majority of genes in any life form encode information for the
production of proteins through the biosynthesis of polypeptide chains from
amino acids having different side groups. Interactions among these side
groups and the environmental conditions cause the proteins to adopt
distinct three-dimensional structures or conformations that are critical to
their functions. Proteins are essential biomolecules that are involved in
almost all biological functions with unparallel versatility in performance:
Numerous different protein molecules take part in a wide variety of task.
Proteins are the main catalysts, structural elements, antibodies, signaling
messengers and molecular machines of cells and biological tissues;
moreover, proteins regulate gene expression for the differential production
of all gene products. In addition, these are often mediated through various
protein-protein interactions. In cancer, which is a disease of genes,
certain key proteins get altered to affect the cellular growth-control
machinery, causing uncontrolled proliferation of the cancer cells. Since
biological and environmental factors influence the gene products, a proper
understanding and use of the 'genome' information necessitate a
comprehensive analysis of the gene products, the 'proteome'. Manipulation
and improvement of proteins and enzymes for their use in chemical,
pharmaceutical, food and other industries are a major application of
biotechnology. Protein biopharmaceuticals which include engineered proteins
and antibodies with improved properties developed and designed for human
therapeutic use, have been synthesized by cloned genes in bacterial or
other suitable host cell systems using modern biotechnology.
Keywords:
Polypeptide; Conformation; Proteomics, Gene expression; Recombinant DNA
technology; Biopharmaceuticals.
PERSPECTIVE
The vast complexity of biological cells, with their varied structures and
ability to perform different tasks are linked to self replication, growth
and development. These are vital to all living systems and are governed by
the same laws of physics and chemistry that determine the behavior of
nonliving systems. While the genetic information is carried by nucleic
acids, the execution of tasks directed by that information is the
responsibility of proteins, which are the most diverse of all
macromolecules. A wide range of protein molecules take part in a variety of
functions. At the chemical level, proteins are polymers of twenty different
amino acids, linked through peptide bonds between the a-amino group of one
amino acid and the a-carboxyl group of the adjacent one; therefore, each
polypeptide chain has two ends, namely the amino terminus and the carboxy
terminus and the length ranging from 50 to more than 1,000 amino acid
residues. The side chains of different L-a-amino acids determine the role
of each amino acid residue in protein structure and function. Thus,
depending on the interactions among these side chains along with the
environmental conditions, proteins adopt distinct three-dimensional (3-D)
structures or conformations that are critical to their functions.
The versatility of proteins is manifested by their remarkable ability to
perform a wide variety of tasks namely, to act as enzymes, transporters,
receptors, binding proteins, scaffolds, signaling molecules and many more,
linking practically all aspects of the life process. Molecular biological
techniques and evolution of modern biotechnology helped to realize the
structure, function, synthesis and regulation of proteins, as well as to
make proteins with desired properties for their use in the medicine, as
biopharmaceuticals.
With an aim to emphasize on the multiple virtues of proteins, this article
will review certain selected areas of cell functions that represent some
major activities of living systems, to depict different roles proteins play
and major attributes of these biomolecules.
PROTEIN AS A CATALYST
A fundamental task of proteins is to act as biocatalysts, enzymes, which
catalyze nearly all chemical reactions within the cells. Cells contain
thousands of different enzymes and their activities determine which of the
many possible chemical reactions actually occur within the cell; even so,
the same basic principles apply to their action: Once a substrate molecule
is bound to the active site of its specific enzyme, multiple mechanisms can
accelerate the conversion of the substrate to the product of the reaction.
The enzyme provides a template upon which the reactants are brought
together and properly oriented to favor the formation of the transition
state in which they interact. Further, this transition state is stabilized
by its tight binding to the enzyme, thereby lowering the required energy of
activation. The catalytic property of a protein resides in the 3-D
structure or conformation resulting from the amino acid sequence encoded by
the gene. Although some reactions can be catalyzed by certain RNAs, most
biological reactions are catalyzed by proteins. [1]
GENE EXPRESSION AND PROTEIN SYNTHESIS
Genomic DNA can be viewed as the set of genetic instructions governing all
cellular activities. From a molecular perspective, the genetic information
residing in the sequence of the four types of nucleotides in the DNA
molecule is expressed via synthesis of RNA by ‘transcription’ process, to
the synthesis of protein by ‘translation’ process. Transcription is
catalyzed by RNA polymerase enzymes and controlled by a number of protein
molecules, called ‘transcription factors’, which ensure faithful copying of
the genetic message from DNA to RNA. Different types of RNA are created by
transcription: these are messenger RNA (mRNA), ribosomal RNA (rRNA) and
transfer RNA (tRNA). Transcription constitutes the primary level of
regulation of gene expression. In eukaryotic organisms, these three types
of RNA are each transcribed by a different RNA polymerase. The process of
translation involves decoding of the codes in mRNA for the synthesis of
polypeptide chains in three distinct phases namely, initiation, elongation
and termination. Translation of mRNA takes place on ribosomes consisting of
specific ribosomal protein (rProtein) and rRNA species and needs amino
acids, tRNA and many specific protein factors for achieving various tasks
in protein synthesis, which is the final step in gene expression.
Regulation of gene expression at protein synthesis level occurs mainly in
the initiation phase and involves interplay of multiple protein factors.
[1, 2]
Exact replication of genomic DNA is crucial for all cells and organisms.
When a cell divides, its entire genome must be duplicated by copying the
large DNA molecule. This requires DNA polymerase enzymes in complex
enzymatic machinery involving many specific protein factors; these are
essential for maintaining the fidelity of replication and integrity of the
newly formed DNA molecules, which must be identical to the parent DNA
molecule. The machinery can also rectify any mistakes during DNA
replication. Additional proteins are needed to repair DNA damage caused by
environmental agents. A failure to maintain the high fidelity of DNA
replication can result in genetic problems including cancer. In all these
processes of replication, transcription and translation, proteins play
major roles through the action of specific enzymes and regulatory factors.
PROTEIN FOLDING AND QUALITY CONTROL
The flow of genetic information within the cell results in the synthesis of
polypeptide chains with amino acid sequence as directed by the nucleotide
sequence of DNA. However, for the formation of active enzymes or other
functional proteins, the polypeptide chains fold into precise 3-D
conformations. A protein folds into a particular shape depending on the
location of its specific amino acid residues and the overall amino acid
composition. Many functional proteins consist of two or more polypeptide
chains as subunits and are termed as homomeric (with same subunits) or
heteromeric (with different subunits) protein molecules. Often large
protein complexes are made up of many different protein components to
perform important cellular functions.
Cells have mechanisms to detect whether the newly synthesized polypeptide
chains are properly folded to their native structure for their necessary
function; those polypeptides which fail are either refolded or degraded.
The central players in this post-translational quality control process for
proteins are chaperons, a class of proteins and proteases. Chaperons
facilitate the initial folding of other proteins by interacting at nascent
polypeptide stage, prevent protein aggregation due to misfolding and
stabilize the released completed protein molecule for folding into its
proper 3-D shape. If a protein does not fold properly, it is recognized as
misfolded; in eukaryotic cells it is degraded by the ubiquitin-proteasome
system. Ubiquitin is a polypeptide involved in the major pathway of
selective protein degradation. Proteins destined for degradation are marked
by ubiquitination (attachment of ubiquitin); the polyubiquitinated proteins
are recognized and degraded by the proteasome, which is a large
multisubunit protease complex; ubiquitin is released and reused. [3, 4]
Disorders in protein folding are the basis of Prion diseases such as
scrapie in sheep, Creutzfeld Jacob disease (CJD) in humans and bovine
spongiform encephalopathy (BSE). The agents that cause these transmissible
diseases are called prions, which are neither cells e.g., bacteria, nor
viruses. Prions are a malfolded form of a cellular protein (PrPc
), which has been remodeled into a protease-resistant, aggregation-prone
and infectivity-associated protein (Prpsc). Prion diseases arise
by errors in PrPc folding due to a templated conformational
remodeling initiated by exposure to PrPsc. [5]
Programmed cell death plays a key role in the maintenance of adult tissues
and embryonic development. It involves a process, known as ‘apoptosis’,
featuring distinct morphological change due to shrinkage and cleavage of
the cell and its chromosomes into fragments, called ‘apoptotic bodies’,
which are subsequently removed by the surrounding cells. The orderly
execution of apoptosis is orchestrated by a family of conserved cysteine
proteases, called caspases, which undergo a cascade of catalytic activation
at the onset of apoptosis and are subject to regulation by yet other
proteins. [6]
POST-TRANSLATIONAL MODIFICATION FOR PROTEIN FUNCTION
After the synthesis of a polypeptide chain in eukaryotic system, it may
reach the site of its intended job or may have to undergo some covalent
modification(s) for its specific job. Such modifications include
phosphorylation, glycosylation, attachment of lipids, disulfide (-S-S-)
bond formation between cysteine residues and partial cleavage of the
peptide chain to smaller chains with distinct functions. The activities of
many cellular proteins are regulated by reversible phosphorylation at
specific sites namely, serine/threonine residues or tyrosine residues by
the action of specific protein kinases and protein phosphatases. Protein
kinases often function in signal transduction pathways by cascading action
such that one kinase activates another, which in turn may activate or
inactivate a third one or a cellular protein. Such sequential action can
transmit a signal received at the cell surface to target proteins within
the cell, causing alterations in cell behavior in response to external
stimuli. The dynamic nature of such phosphorylation steps involving
multiple sites contributes to precise tuning of the protein factor(s) as
key to the signal incorporation and intricate cellular control. [1, 7]
MEMBRANE PROTEINS
Membrane proteins reside and function at the interface to the adjacent
medium. They play vital roles as cell receptors, transporters, channels and
as essential components of respiratory complexes. The cell membrane is
heterogeneous and is composed mainly of phospholipid bilayer; while the
polar heads define the lipid-water interphases, its hydrophobic part forms
the core of the membrane. Because of constraints in this complex
hydrophobic environment, the transmembrane domains of the membrane proteins
fold and the a-helical type proteins are most abundant. Different classes
of membrane receptor proteins take part in the transmission of
extracellular signals inside the cell for regulating the cell activities.
Many such receptors belong to the super family of G-protein coupled
receptors (GPCRs) that mediate taste, smell, vision, and the effects of
most hormones and neurotransmitters. They are important for biomedical and
pharmaceutical research as potential targets for therapeutic intervention;
they are the primary site of action of many life-saving drugs and are
target for future development. [8-10]
ANTIBODIES
Antibodies are immunoglobulin proteins produced in animals as a defence
mechanism in response to foreign materials, called antigens.
Immunoglobulins consist of mainly two types of polypeptides, called heavy
(H) chains and light (L) chains, which form Y-shaped molecules. The amino
terminal regions of both H and L chains of an antibody molecule bear highly
variable sequence, evolved to bind an antigen molecule very specifically
and tightly. Injection of an antigen in experimental animals can produce
antibodies with the capacity to bind the antigen molecules with exquisite
specificity and high affinity. Owing to their specificity, affinity and
ease of production, antibodies are critical reagents in many experiments as
well as for analytical, preparative and diagnostic procedures. Monoclonal
antibodies, which can recognize and bind specific single minute chemical
parts of an antigen, have been developed for application in research and
medicine. [10]
CYTOSKELETAL PROTEINS
The cytoskeleton consists of a network of protein filaments extending
throughout the cytoplasm of all eukaryotic cells and is composed of
microfilaments, intermediate filaments and microtubules with diameters
7-9.5 nm, 10-12 nm and 25 nm respectively; these are held together and
linked to subcellular organelles and plasma membrane with a variety of
accessory proteins. It provides a structural framework as a scaffold for
the cell.
The major cytoskeletal protein of most cells is actin, which polymerizes to
form microfilaments. Actin bundles arise when small rigid proteins, called
actin-bundling proteins force the filaments to align closely with one
another. Conversely, the proteins that organize actin filaments into
network appear to be large flexible modular proteins that can crosslink
perpendicular filaments. Many types of cell movements are due to actin
filaments, usually in association with myosin, as the prototype of a
molecular motor and play a central role in cell biology. Intermediate
filaments are composed of a variety of proteins expressed in different
types of cells. They appear to play a structural role by providing
mechanical strength to cells and tissues.
Microtubules are hollow cylindrical and dynamic structures, assembled from
their building block protein tubulin, and undergo assembly and disassembly
depending on necessity within the cell. Microtubules constitute the mitotic
spindle and therefore, play a central role in mitosis. They also execute in
cell shape, cell movements, intracellular transport of organelles,
separation of chromosomes during mitosis, and the beating of cilia and
flagella. The dynamic behavior of microtubules within the cell is
influenced by interactions with several proteins. Some cellular proteins
(stathmin in certain cancers) can disassemble microtubules, while some
other proteins, called microtubule-associated proteins (MAPs) bind to
microtubules and increase their stability. Certain antimitotic drugs for
cancer therapy act by interfering with the microtubule system. [1, 10, 11]
PROTEIN FUNCTION AND PROTEIN-PROTEIN INTERACTION
Protein function typically depends on a subset of its amino acid residues
and is commonly mediated by regions on the surface that interact with
external factors such as substrates, ligands, or specific nucleic acid
sequences. The concept of protein function and its understanding can vary
largely depending on the functional level under consideration (molecular,
cellular, physiological etc.). The classic view of protein function focuses
on the action of a single protein molecule, either in the catalysis of a
given reaction, or in the binding of a small or large molecule. This is
sometimes termed as ‘molecular’ function of the protein, in an attempt to
distinguish it from an expanded view of function, termed as ‘contextual’ or
‘cellular’ function, where a protein is an element in the network of its
interactions. Each protein in living matter functions as part of an
extended web of interacting molecules. Since most cellular processes are
regulated by multiprotein complexes, the interactions among proteins play a
vital role in determining all the biological events in organisms. Several
approaches have so far been made to understand these protein-protein
interactions. Genomic studies and high throughput methods of the
postgenomic era may shed a new light on the protein function. The analysis
of large protein-protein networks also may permit the emergence of a more
integrated view of protein functions. [12, 13]
The complete genomic sequencing of a number of species ranging from
bacteria and viruses to plants and human has yielded vast data on genetic
information, genetic maps, nucleotide sequence and markers. Yet, such
genetic information does not necessarily match by quantity or quality at
the protein levels, because biological and environmental factors influence
the gene products. So, a comprehensive analysis of the gene products,
meaning a study of the ‘proteome’, is essential for a proper understanding
and application of the genome information. The proteome may be defined as
the time- and cell-specific protein complement of the genome and it covers
all proteins that are expressed in a cell at one time, including isoforms
and protein modifications. Thus, organism complexity is generated more by a
complex proteome than by a complex genome. While genome is constant and
largely identical for all cells of an organism, the proteome is more
variable with time and significantly differs between cell types, in
response to external stimuli. Proteomics or proteome analysis in general
involves methods of protein analysis viz., 2-D gel electrophoresis, mass
spectrometry; protein identification using databases; biochemical
characterization of proteins of unknown function by amount, localization,
structure, post-translational modification, antibody binding, etc. [10, 13,
14]
CANCER AND CELL TRANSFORMATION
The fundamental abnormality resulting in the development of cancer is the
continual uncontrolled proliferation of cancer cells with lack of
inhibition by cell-cell contact, defective differentiation and reduced
requirements for extracellular growth factors. Cancer is a disease of
genes, which is caused by diverse factors or carcinogens, viz., certain
chemicals, radiations and specific viruses; these affect the host’s genetic
system through mutations with rearrangements or deletions of specific genes
to result in uncontrolled growth of cells or tissues to produce tumors and
metastasis. The characteristic immortality of cancer cells is due to their
failure in apoptosis that contributes substantially to tumor development.
Cancer cells typically display defects in the regulation of cell
proliferation, differentiation and survival. These abnormalities arise due
to activation of cancer causing genes (oncogenes) and/or inactivation of
tumor suppressor genes and their respective products, called oncoproteins
and tumor-suppressor proteins. The uncontrolled proliferation of cancer
cells in vivo is mimicked by their behavior in cell culture. Tumor
viruses, which cause cancer in humans and experimental animals, have played
a critical role in cancer research by serving as models for cellular and
molecular studies of cell transformation i.e., the conversion of normal
cells to tumor cells in culture. These have been contributing to our
current understanding of cancer at the molecular level. [15]
Progress in molecular biology research is driving the pharmaceutical
R&D towards the development of new inhibitors of the cell division
cycle, where most factors are controlled by protein-phosphorylation
/dephosphorylation events. The main players in such controls are a group of
related protein kinases (specifically, protein-serine/threonine kinases)
named ‘cyclin-dependent kinases’ (CDKs) and their regulatory subunit
proteins, called ‘cyclins’. The activities of CDKs are regulated in several
ways e.g., by differential phosphorylation at several sites on the CDK
proteins, expression and degradation of respective cyclins, and by the
binding of inhibitory proteins, called CDK inhibitors. Cyclins and CDKs are
among the most extensively studied potential targets for developing drugs
against cancer since the tumor cells evade the cell cycle control and
exhibit false checkpoints in favor of their proliferation. [10, 14]
BIOTECHNOLOGICAL APPROACHES
Biotechnology is a multidisciplinary science and has many applications. It
offers the tools for manipulation and improvement of proteins and enzymes
through the use of gene cloning or recombinant DNA technology. A major
application involves the use of enzymes in chemical, pharmaceutical, food
and other industries. By virtue of their specificity and ability to
catalyze chemical reactions under relatively mild conditions, enzymes have
found many industrial applications, helping to avoid the use of harsh
chemicals and process patterns. Enzyme production in large amounts and with
required properties has been revolutionized by the developments and
applications of recombinant DNA technology, which have paved the path of
modern biotechnology. [16, 17]
HETEROLOGOUS PROTEINS BY GENE CLONING
Numerous proteins of heterologous origin have been effectively expressed in
genetically engineered prokaryotic host cells. Nevertheless, many proteins
of eukaryotic sources need to undergo specific post-translational
modifications (such as glycosylation), to be functional. For production of
such recombinant proteins in large quantities for research or industrial
use, good expression systems have been devised using a number of eukaryotic
hosts e.g., yeast, filamentous fungus, insect, plant and mammalian cells in
culture and organisms. Each of these systems offers distinct advantages and
disadvantages. In practical terms, however, there is no single eukaryotic
expression system that is capable of producing an authentic protein from
every cloned gene.
Although the primary objective of gene cloning is the expression of the
cloned gene in a selected host organism, the insertion of a gene into a
cloning vector does not necessarily ensure that it will be successfully
expressed. The production of a protein requires that the gene be properly
transcribed and the mRNA be translated. High expression vectors have been
created with genetic elements for controlling transcription, translation,
protein stability and secretion of the product of the cloned gene from the
host cell. [14, 16, 18]
PROTEIN ENGINEERING
A major reason for the relatively low number of industrially usable enzymes
is that an enzyme, evolved for a particular function in biological cell
under natural condition, may not be suitable for a specialized industrial
application. This is because most enzymes are prone to denaturation due to
loss of their 3-D structure or conformation on exposure to relatively harsh
conditions viz., high temperature, extreme pH or organic solvents that are
used in many industrial processes.
The unique properties of a protein reside in its correctly folded, 3-D
structure, which in turn is an outcome of the sequence of its amino acids
encoded by the gene for the protein. Certain amino acids at some specific
positions in a protein chain can play important role in determining the
specificity, thermostability and other properties of a protein. Changing
even a single nucleotide of the gene can cause incorporation of a different
amino acid than the original one. This may result in either disruption of
the normal activity, or enhancement of a specific property of the protein.
Protein engineering techniques that involve directed mutagenesis and
recombinant DNA technology can selectively alter or replace any nucleotide
of a cloned gene for producing proteins with specific amino acid
replacement at the chosen site. The selection of amino acid for replacement
is based on the knowledge of the amino acid’s role in the functional
protein and this knowledge is gained through genetic studies, or X-ray
crystallographic data of the 3-D structure of the protein. Applications of
protein engineering in the pharmaceutical industry have led to the
development of engineered proteins and antibodies with improved properties
e.g., immunotoxins and immunolysins for the treatment of cancer, with an
objective that these drugs will attack only the cancer cells and reduce the
unpleasant side effects. [1, 14]
BIOPHARMACEUTICALS
The term “biopharmaceuticals” denote biotechnologically derived drug
products. The 20th century saw the golden age for the discovery and
synthesis of chemical entities, drugs and medicines; the present century is
seen as era of drugs from biomaterials, particularly from biotechnology.
The foundation of modern biotechnology was built by enhanced understanding
of protein structure, metabolic regulation and gene expression that led to
the discovery and use of restriction enzymes in recombinant DNA technology,
and the invention of monoclonal antibodies (MAbs) through hybridoma
technology.
Recombinant technology enabled the production of a wide range of natural
and modified proteins in large quantities. Previously, the dependence on
the extraction from natural sources severely limited the range and quantity
of proteins available for clinical use. The earliest recombinant products
were replacements for existing protein products, which were extracted from
animal sources. Insulin was the first recombinant protein (approved in
1982); next were growth hormone, blood-clotting factor VIII, cytokines,
growth factors, receptor antagonists, enzymes and antibodies. Hybridoma
technology created new proteins namely MAbs that provided an alternative
approach to treat many diseases.
Gene technology has also made it possible to produce proteins, engineered
with improved characteristics. Insulin analogs with altered amino acid
sequences have been developed to affect the speed of hormone action: For
example, insulin lispro and insulin aspart are fast acting analogs in which
specific amino acids at the C-terminal were changed to reduce the
self-association properties of insulin; insulin glargine is a long-acting
variant that dissociates slowly from microcrystalline precipitate. These
analogs enable better control of insulin availability based on clinical
circumstances. [19, 20]
The second generation of products include recombinant proteins and MAbs
which represent the largest and fastest growing category of
biopharmaceutical proteins with applications in the cancer field; immune
disorders and infectious diseases. Various approaches have been used to
modify therapeutic activity of proteins, improve their stability, or reduce
the rate of their clearance. These include amino acid substitutions, domain
removal, fusion of peptide sequences from different proteins, and
glycosylation engineering. Protein engineering techniques have been applied
to MAbs for antibody humanization. PEGylation has been used to modify
protein properties and to prevent proteolytic degradation and the rate of
in vivo clearance.
Stabilizing the protein’s native folded structure during storage is
essential to maintaining the biologic activity. Ideally, the purpose of
formulation development of biopharmaceutical protein therapeutics is to
provide a final dosage form that offers sufficient ex vivo
stability during processing, handling and long-term storage, and also
provide adequate in vivo stability in terms of bioavailability
that meets the pharmacokinetics / pharmacodynamics (PK/PD) therapeutic
requirements. [20, 21]
Proteins are the most important class of receptors which are also excellent
targets for drugs. Molecular cloning of receptor proteins is useful for
gaining an insight of fundamental structural motifs; identifying novel
receptors and isoforms of receptors; expression and purification of various
classes of receptors, transducers and effector proteins; and understanding
their biochemical mechanisms. The future of drug discovery depends on an
understanding the genetic basis of the disease.
A better understanding of biological systems leads to a dramatic increase
in targets for drug development. Genomic revolution has been a key factor
for driving the future developments through innovations in modern
biotechnology. In the future, as ‘drugs’ become more complex and difficult
to deliver – to cross the biological membranes to reach the target – novel
drug delivery becomes very important as a critical component of drug
research. New approaches to drug targeting are developed using monoclonal
antibody, or a carrier-system or device for transporting the drug to a
specific target site by means of liposomes, nanoparticles etc.
Perhaps the greatest beneficiary of the advancement of biotechnology has
been the pharmaceutical industry. There is a rise in biopharmaceutical
sales and the requirement of protein based drugs. The development of such
products places increased emphasis on improving existing technologies,
process efficiencies and yields.
CONCLUDING REMARKS
The vast majority of genes in any life form encode information for the
production of proteins through the biosynthesis of polypeptide chains.
Proteins are essential biomolecules that are involved in almost all
biological functions with unparallel versatility in performance: They
catalyze chemical reactions; take part in cell-cell communication and
signal transduction; transport molecules within and between cells; provide
support to cells, organs and body structures; cause movement; render
protection against infectious agents and toxins; and regulate gene
expression for the differential production of all gene products, including
their own !
Modern protein research seems to put major thrusts on: i) Understanding
proteins as molecular machines; this needs detailed analysis of protein
structure and function at the molecular level. ii) Identifying the spectrum
of proteins synthesized by the time- and situation-specific differential
expression of genes in the genome; the emergence of proteomics has
attracted those involved in the drug discovery. iii) Manipulation and
improvement of enzymes; optimization as commercial biocatalysts for
industrial application. iv) Developments in biopharmaceutical proteins and
their expression for human therapeutic use; expression systems with
modified lower eukaryotic cells (as substitute of mammalian cells in
culture). Nevertheless, the ultimate objective of all biotechnology
research is the development of commercial products/processes and is
therefore, driven to a great extent by economics.
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