SEQUENCE SIMILARITIES WITHIN THE FAMILY OF DIHYDROLIPOAMIDE ACYLTRANSFERASES AND DISCOVERY OF A PREVIOUSLY UNIDENTIFIED FUNGAL ENZYME

A composite protein sequence database was searched for amino acid sequences similar to the C-terminal domain of the dihydrolipoamide acetyltransferase subunit (E2p) of the pyruvate dehydrogenase complex of Escherichia coli. Nine sequences with extensive similarity were found, of which eight were E2 subunits. The other was for a putative mitochondrial ribosomal protein, MRP3, from Neurospora crassa. Alignment of the MRP3 and E2 sequences showed that the similarity extends through the entire MRP3 sequence and that MRP3 is most closely related to the E2p subunit of the pyruvate dehydrogenase complex from Saccharomyces cerevisiae, with 54% identical residues and a further 36% that are conservatively substituted. Other features of the MRP3 gene and protein are also consistent with it being the acyltransferase subunit of a 2-oxo acid dehydrogenase complex. A multiple alignment of 13 E2 sequences indicated that 120 (34%) of 353 equivalenced residues are identical or show some degree of conservation. It also identified residues that are potentially important for the structure, catalytic activity and substrate-specificity of the acyltransferases.