Trimethyllysine and protein function. Effect of methylation and mutagenesis of lysine 115 of calmodulin on NAD kinase activation.

Unmethylated calmodulins have been enzymatically methylated at lysine 116, and a direct effect of this methylation on NAD kinase activation has been shown.Similar to naturally occurring calmodulins with trimethyllysine 115, the enzymatically methylated calmodulins activated an NAD kinase preparation to a maximal level that was at least $fold lower than the level of activation obtained with the corresponding unmethylated calmodulins.Methylation did not alter the cyclic nucleotide phosphodiesterase activator properties of these calmodulins.A genetically engineered calmodulin containing an arginine at position 11 5 instead of a lysine was produced by site-specific mutagenesis of a cloned synthetic calmodulin gene.The arginine derivative retained the higher maximal NAD kinase activator properties of the unmethylated calrnodulins but was no longer susceptible to the effects of the methyltransferase.The data indicate that the reduction in the level of NAD kinase activation is the direct result of trimethylation of lysine 115 of calmodulin, provide a precedent for a functional effect of trimethyllysine in a protein, and raise the possibility that some of calmodulin's physiological activities may be affected by lysine methylation.Methylation of specific lysine residues in proteins is a widespread phenomenon (1).Among the diverse groups of proteins that possess methylated lysine residues is the eukaryotic calcium-modulated protein, calmodulin, which in many cases contains W-trimethyllysine at position 115 (2-5).Similar to other proteins that have methylated lysine residues, the functional significance of trimethyllysine in calmodulin action is not known.Active calmodulins that lack this posttransla-Grant GM30861 (to D. M. W.) and Grants NS11652 and HD03352 *