cysteinylAMP

CysteinylAMP, also called cysteinyl-adenylate, is an aminoacyl-adenylate intermediate formed during the activation of the amino acid cysteine by the enzyme cysteinyl-tRNA synthetase. This enzyme is part of the broader family of aminoacyl-tRNA synthetases that couple amino acids to their corresponding tRNAs for use in translation.

The activation proceeds in two steps. First, cysteine reacts with ATP in the enzyme’s active site to form cysteinyl-AMP and inorganic pyrophosphate. In the second step, the cysteinyl moiety is transferred from cysteinyl-AMP to the 3′-OH group of the terminal adenosine of tRNA^Cys, producing cysteinyl-tRNA^Cys and AMP. The cysteinyl-AMP intermediate is highly reactive and is typically short-lived, serving as a transient carrier of activated cysteine to the tRNA.

CysteinylAMP is not usually isolated under physiological conditions; its existence is inferred from kinetic and structural studies of cysteinyl-tRNA synthetase. The reaction ensures high-fidelity incorporation of cysteine into proteins during translation, with the enzyme’s editing and quality-control mechanisms helping to prevent misactivation of closely related amino acids. The cysteinyl-tRNA synthetase–cysteinylAMP pathway is conserved across many organisms, reflecting the essential role of accurate aminoacylation in protein synthesis.