Hydrophobic collapse
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Hydrophobic collapse is a proposed process for the production of the 3-D conformation adopted by polypeptides and other molecules in polar solvents. The theory states that the nascent polypeptide forms initial secondary structure (ɑ-helices and β-strands) creating localized regions of predominantly hydrophobic residues. The polypeptide interacts with water, thus placing thermodynamic pressures on these regions which then aggregate or "collapse" into a tertiary conformation with a hydrophobic core. Incidentally, polar residues interact favourably with water, thus the solvent-facing surface of the peptide is usually composed of predominantly hydrophilic regions.[1]
Hydrophobic collapse may also reduce the affinity of conformationally flexible drugs to their protein targets by reducing the net hydrophobic contribution to binding by self association of different parts of the drug while in solution. Conversely rigid scaffolds (also called privileged structures) that resist hydrophobic collapse may enhance drug affinity.[2][3][4]
Partial hydrophobic collapse is an experimentally accepted model for the folding kinetics of many globular proteins, such as myoglobin,[5] alpha-lactalbumin,[6] barstar,[7] and staphylococcal nuclease.[8] However, because experimental evidence of early folding events is difficult to obtain, hydrophobic collapse is often studied in silico via molecular dynamics and Monte Carlo simulations of the folding process.[9][10] Globular proteins that are thought to fold by hydrophobic collapse are particularly amenable to complementary computational and experimental study using phi value analysis.[11]
Correct protein folding is integral to proper functionality within biological systems. Hydrophobic collapse is one of the main events necessary for reaching a protein's stable and functional conformation. Proteins perform extremely specific functions which are dependent on their structure. Proteins that do not fold correctly are nonfunctional and contribute nothing to a biological system.
Hydrophobic aggregation can also occur between unrelated polypeptides. If two locally hydrophobic regions of two unrelated structures are left near each other in aqueous solution, aggregation will occur. In this case, this can have drastic effects on the health of the organism. The formation of amyloid fibrils, insoluble aggregates of hydrophobic protein can lead to a myriad of diseases including Parkinson's and Alzheimer's disease.[12]
