Abstract
Cys is much different from other common amino acids in proteins. Being one of the least abundant residues, Cys is often observed in functional sites in proteins. This residue is reactive, polarizable, and redox-active; has high affinity for metals; and is particularly responsive to the local environment. A better understanding of the basic properties of Cys is essential for interpretation of high-throughput data sets and for prediction and classification of functional Cys residues. We provide an overview of approaches used to study Cys residues, from methods for investigation of their basic properties, such as exposure and pK(a), to algorithms for functional prediction of different types of Cys in proteins.
Highlights
Another unique property of Cys is its ability to functionally interchange with Sec
Cys thiols are capable of unique reactivity in the protein world: covalent interactions with other thiols create intra- and intermolecular disulfide bonds
The side chain of Cys can directly react with many oxidants or oxidized cellular products under physiological and pathophysiological conditions: reversible oxidation of Cys thiols is known to play a role in redox regulation of proteins via the formation of sulfenic acid intermediates [13,14,15], mixed disulfides with glutathione [16], and overoxidation to sulfinic acids [17]
Summary
We provide an overview of approaches used to study Cys residues, from methods for investigation of their basic properties, such as exposure and pKa, to algorithms for functional prediction of different types of Cys in proteins. Similar electrostatic changes can affect the ability of a protein to interact with the environment, for instance, with other proteins and charged molecules This observation highlights the intrinsically high responsiveness of exposed Cys to changes in physiological states and environmental conditions, an aptitude that may provide a biological (more so than chemical or physical) explanation for why Cys residues are found much less frequently (than expected) on molecular surfaces. A pKa shift is evaluated as a function of the sum of energy contributions provided by surrounding residues
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