Abstract
A guanine nucleotide-dependent protein carboxyl methylation is demonstrated in mammalian cell membranes. The methylation of membrane proteins of Mr 20,000-23,000 requires S-adenosylmethionine, GTP or nonhydrolyzable GTP analogs, and a cytoplasmic methyltransferase. The protein methyl groups are stable at neutral pH and under basic conditions hydrolyze to produce methanol. The specific methyl acceptor proteins and methyltransferases varied between tissues and cell types, suggesting that these methylations have cell-specific functions. The guanine nucleotide-dependent carboxyl methylations provide a possible mechanism for regulating the function of GTP-binding membrane proteins in the transduction of receptor-mediated signals of eukaryotic cells.
Highlights
Biochemistry, National Instituteof Mental Health, Here, we demonstrate that several membrane proteins can Bethesda, Maryland 20892 be carboxyl methylated by S-adenosylmethionine in an enzymatic reaction that is greatly stimulated by the presence of
The guanine nucleotide dependence and the physiologically reversible nature of carboxyl methylations suggest that these methylations may regulate the function of some guanine nucleotide-binding membrane proteins
Several guanine nucleotide-binding proteins have determine if the methyltransferases were localized to specific been purified, and there is a large range in the levels present cells
Summary
Biochemistry, National Instituteof Mental Health, Here, we demonstrate that several membrane proteins can Bethesda, Maryland 20892 be carboxyl methylated by S-adenosylmethionine in an enzymatic reaction that is greatly stimulated by the presence of. Several families of guanine nucleotide-binding proteins have been characterized, including the G-protein [16] and ras-protein resuspended in 0.5 ml of ice-cold 0.1 M sodium phosphate, pH 6.8, and the membranes were pelleted and resuspended two additional times. [rnethyt-3H]S-adenosylmethioninien the presence of the cytosol fraction from RAW264 cells, and the incorporation of radioactivity was determined after separation of the proteins by SDS-polyacrylamide gel electrophoresis.
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