LIPOYLATION OF H-PROTEIN OF THE GLYCINE CLEAVAGE SYSTEM - THE EFFECT OF SITE-DIRECTED MUTAGENESIS OF AMINO-ACID-RESIDUES AROUND THE LIPOYLLYSINE RESIDUE ON THE LIPOATE ATTACHMENT

H-protein of the glycine cleavage system has lipoic acid on the Lys59 residue. Comparison of amino acid sequences around the lipoate attachment site of H-proteins from various sources and acyltransferases of alpha-keto acid dehydrogenase complexes indicated that Gly43, Glu56, Glu63 and Gly70 of bovine H-protein are highly conserved among these proteins. Modification of these conserved residues by site-directed mutagenesis indicated that Glu56 and Gly70 are important for the lipoylation of H-protein and suggested that the proper conformation around the lipoic acid attachment site is required for the association of H-protein to the enzyme responsible for the lipoylation.