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Chemical biology is a scientific discipline spanning the fields of chemistry and biology that involves the application of chemical techniques and tools, often compounds produced through synthetic chemistry, to the study and manipulation of biological systems. This is a subtle difference from biochemistry, which is classically defined as the study of the chemistry of biomolecules. For example, a biochemist would seek to understand the three-dimensional structure of a protein and how that structure relates to the chemistry of the protein. Chemical biologists attempt to utilize chemical principles to modulate systems to either investigate the underlying biology or create new function. In this way, the research done by chemical biologists is often closer related to that of cell biology than biochemistry. In short, biochemists deal with the chemistry of biology, chemical biologists deal with chemistry applied to biology.
Introduction
Some forms of chemical biology attempt to answer biological questions by directly probing living systems at the chemical level. In contrast to research using biochemistry, genetics, or molecular biology, where mutagenesis can provide a new version of the organism or cell of interest, chemical biology studies sometime probe systems in vitro and in vivo with small molecules that have been designed for a specific purpose or identified on the basis of biochemical or cell-based screening.
Chemical biology is one of many
Systems of interest
Proteomics
After the completion of the
The global analysis of the proteome is called
Another challenge of chemical biology is to decipher the myriad signal transduction pathways involving kinase and phosphatase signaling. In this regard, Kevan Shokat at UCSF has developed a method for selectively inhibiting a given kinase upon the addition of an otherwise biologically orthogonal competitive inhibitor (1-napthylmethyl-PP1)[1]. Shokat's technique involves altering a protein kinase (by mutating the so-called "gatekeeper" residue in the kinase catalytic domain) to contain an unnatural hydrophobic binding pocket which distinguishes it from the other highly homologous cellular kinases, allowing it to be selectively inhibited. A related method has been developed in his lab which uses these so-called "analog-sensitive" kinases to label their substrates using an unnatural ATP (adenosine triphosphate) analog, facilitating their visualization and identification. Identification of enzyme substrates (of which there may be hundreds or thousands, many of which are unknown) is a problem of significant difficulty in proteomics and is vital to the understanding of signal transduction pathways in cells; techniques for labelling cellular substrates of enzymes are a typical approach used by chemical biologists to address this problem.
Many researchers are working on ways to manipulate the way that proteins are assembled by cellular systems. In this regard,
Glycobiology
While
Combinatorial chemistry
Some chemical biologists use automated synthesis of many diverse compounds in order to experiment with effects of small molecules on biological processes. More specifically, they observe changes in the behaviors of proteins when small molecules bind to them. Such experiments may supposedly lead to discovery of small molecules with antibiotic or chemotherapeutic properties. These approaches are identical to those employed in the discipline of Pharmacology.
Molecular Sensing
Chemical biologists are also interested in developing new small-molecule and biomolecule-based tools to study biological processes, often by molecular imaging techniques. Today, researchers continue to utilize basic chemical principles to develop new compounds for the study of biological metabolites and processes.
Employing biology
Many research programs are also focused on employing natural biomolecules to perform a task or act as support for a new chemical method or material. In this regard, researchers have shown that DNA can serve as a template for synthetic chemistry, self-assembling proteins can serve as a structural scaffold for new materials, and RNA can be evolved in vitro to produce new catalytic function.
Protein Misfolding and Aggregation as a Cause of Disease
Through the
Normally when a protein does not fold correctly,
A common form of aggregation is long, ordered spindles called amyloid fibrils which are implicated in Alzheimer’s disease which have been shown to consist of cross-linked
Protein misfolding has previously been studied using both computational approaches as well as in vivo biological assays in
Dobson et al. propose combining these two approaches such that computational models based on the organism studies can begin to predict what factors will lead to protein misfolding[7]. Several experiments have already been performed based on this strategy. In experiments on Drosophila, different mutations of beta amyloid peptides were evaluated based on the survival rates of the flies as well as their motile ability. The findings from the study show that the more a protein aggregates, the more detrimental the neurological dysfunction [7][8][9]. Further studies using tranthyretin, a component of cerebrospinal fluid which binds to beta amyloid peptide deterring aggregation but can itself aggregate especially when mutated, indicate that aggregation prone proteins may not aggregate where they are secreted and rather are deposited in specific organs or tissues based on each mutation[10]. Kelly et al. have shown that the more stable, both kinetically and thermodynamically, a misfolded protein is the more likely the cell is to secrete it from the endoplasmic reticulum rather than targeting the protein for degradation.[11] Additionally, the more stress that a cell feels from misfolded proteins, the more probable new proteins will misfold[12]. These experiments as well as others having begun to elucidate both the intrinsic and extrinsic causes of misfolding as well as how the cell recognizes if proteins have folded correctly.
As more information is obtained on how the cell copes with misfolded proteins, new therapeutic strategies begin to emerge. An obvious path would be prevention of misfolding. However, if protein misfolding cannot be avoided, perhaps the cell’s natural mechanisms for degradation can be bolstered to better deal with the proteins before they begin to aggregate[13]. Before these ideas can be realized, many more experiments need to be done to understand the folding and degradation machinery as well as what factors lead to misfolding. More information about protein misfolding and how it relates to disease can be found in the recently published book by Dobson, Kelly, and Rameriz-Alvarado entitled Protein Misfolding Diseases Current and Emerging Principles and Therapies[14].
Protein Design by Directed Evolution
One of the primary goals of
Several methods exist for creating large libraries of sequence variants. Among the most widely used are subjecting
There are two general strategies for choosing the starting sequence for a directed evolution experiment: de novo design and redesign. In a protein design experiment, an initial sequence is chosen at random and subjected to multiple rounds of directed evolution. This has been employed successfully to create a family of ATP-binding proteins with a new folding pattern not found in nature.[21] Random sequences can also be biased towards specific folds by specifying the characteristics (such as polar vs. nonpolar) but not specific identity of each amino acid in a sequence. Among other things, this strategy has been used to successfully design four-helix bundle proteins [22][23]. Because it is often thought that a well-defined structure is required for activity, biasing a designed protein towards adopting a specific folded structure is likely to increase the frequency of desirable variants in constructed libraries.
In a protein redesign experiment, an existing sequence serves as the starting point for directed evolution. In this way, old proteins can be redesigned for increased activity or new functions. Protein redesign has been used for protein simplification, creation of new quaternary structures, and topological redesign of a
Computational methods, when combined with experimental approaches, can significantly assist both the design and redesign of new proteins through directed evolution. Computation has been used to design proteins with unnatural folds, such as a right-handed coiled coil.[30] These computational approaches could also be used to redesign proteins to selectively bind specific target molecules. By identifying lead sequences using computational methods, the occurrence of functional proteins in libraries can be dramatically increased before any directed evolution experiments in the laboratory.
Publications
- ACS Chemical Biology - The new Chemical Biology journal from the American Chemical Society.
- Bioorganic & Medicinal Chemistry - The Tetrahedron Journal for Research at the Interface of Chemistry and Biology
- ChemBioChem – A European Journal of Chemical Biology
- Chemical Biology- A point of access to chemical biology news and research from across RSC Publishing
- Chemistry & Biology - An interdisciplinary journal that publishes papers of exceptional interest in all areas at the interface between chemistry and biology.
- Journal of Chemical Biology - A new journal publishing novel work and reviews at the interface between biology and the physical sciences, published by Springer.
- Journal of the Royal Society Interface - A cross-disciplinary publication promoting research at the interface between the physical and life sciences
- Molecular BioSystems- Chemical biology journal with a particular focus on the interface between chemistry and the -omic sciences and systems biology.
- Nature Chemical Biology - A monthly multidisciplinary journal providing an international forum for the timely publication of significant new research at the interface between chemistry and biology.
- Wiley Encyclopedia of Chemical Biology
References
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- ^ http://pubs.acs.org/doi/abs/10.1021/cb700248m
- ^ http://nobelprize.org/nobel_prizes/chemistry/laureates/2008/index.html
- ^ Jordens, S., Adamick, J., Amar-Yuli, I., and Mezzenga, R. (2010) Disassembly and Reassembly of Amyloid Fibrils in Water−Ethanol Mixtures, In Biomacromolecules, ACS Publications. DOI:http://dx.doi.org/10.1021/bm101119t
- ^ Reddy, G., Straub, J. E., and Thirumalai, D. (2010) Dry amyloid fibril assembly in a yeast prion peptide is mediated by long-lived structures containing water wires, Proceedings of the National Academy of Sciences of the United States of America 107, 21459-21464. DOI: http://dx.doi.org/10.1073/pnas.1008616107
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External links
- Chemical Biology - BioChemWeb.org
- Chemical Biology Doctoral Training Centre, Imperial College London