Structural Consensus Rules for Cysteine Protease Inhibition by NO(-Donors)

Nitric oxide (NO) exerts its action in several physiological and pathological events. The great propensity for Cys(NO)-(de)nitrosylation represents a mechanism which modulates cysteine protease action. Cys(NO)-(de)nitrosylation is assisted by basic and acid residues, within the environment of the Cys catalytic residue. In particular, Cys-nitrosylation is catalyzed by amino acid residues which stabilize the reactive deprotonated form of the Cys Sγ atom. By contrast, CysNO-denitrosylation is assisted by amino acid residues which facilitate the protonation of the Cys Sγ atom with the concomitant NO release. Note that Cysnitrosylated residues may undergo oxidation giving rise to sulfenic, sulfinic or sulfonic acid and lead to the formation of disulfide bridges. These structural consensus rules apply not only to cysteine proteases, but represent a generally accepted mechanism for (macro)molecular Cys(NO)-(de)nitrosylation.