Perspectives on the biological function and enzymology of protein carboxyl methylation reactions in eucaryotic and procaryotic cells.

Abstract

Enzymes have been detected in all cells examined so far that catalyze the incorporation of methyl groups from S-adenosylmethionine into base-labile linkages on proteins. Although the products of these reactions have many of the properties of methyl esters, their frequent instability has often precluded direct analysis of the linkage chemistry. As a result, previous studies of “protein carboxyl methyltransferase” have included representatives of what has turned out to be at least two distinct classes of enzymes. The often mentioned specificity of such an activity for aspartyl and glutamyl residues is based largely on the apparent chemical reasonableness of such assignments, and specific evidence for the methylation of such residues has rarely been presented. The lack of specific knowledge on the chemistry of such modification reactions has been accompanied by a similar lack of understanding of their physiological role (for reviews of the earlier literature see Gagnon and Heisler, 1979; Borchardt, 1980; Paik and Kim, 1980; O’Dea et al., 1981; Clarke, 1985).