Different types of interactions involving cysteine sulfhydryl group in proteins.
Various types of interactions involving the sulfhydryl group of free cysteine residues have been analyzed using known protein structures. In a hydrogen bond the -SH group is more amenable to donating its proton to a carbonyl group, rather than acting as a proton acceptor. It rarely interacts with a carboxylate group, and is a poor ligand to bind an anionic substrate. It is quite prone to make contacts that are definitely non-hydrogen bond type. In the S...C=O interaction the S atom is placed on the face of an amide group (mostly from the main-chain, but there are cases from the side-chain also) close to the C atom. Cases of S...N interaction, where the S atom is on top of the N atom of another residue (both main-, as well as side-chains, including the guanidinium group) are also observed. A considerable number of Cys residues have aromatic residues as neighbors, and here too, the preferred mode of interaction is along the face. The intra-residue S...C=O interaction constrains the main-chain and side-chain torsion angles (psi and chi1), whereas the inter-residue interactions are non-local and stabilize the tertiary structure. The S...C=O interaction may have a role in lowering the pKa values of the Cys residues in enzyme active sites.
Department of Biochemistry, Bose Institute, CIT Scheme VIIM, Calcutta, India.
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Chakrabarti
D002244:Carbon; D003545:Cysteine / Q000378:metabolism*; D006860:Hydrogen Bonding; D009584:Nitrogen; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D013438:Sulfhydryl Compounds / Q000737:chemistry / Q000378:metabolism*; D013455:Sulfur
D011506:Proteins; D013438:Sulfhydryl Compounds; D013455:Sulfur; D002244:Carbon; D003545:Cysteine; D009584:Nitrogen