SIMILARITY BETWEEN SERINE HYDROXYMETHYLTRANSFERASE AND OTHER PYRIDOXAL PHOSPHATE-DEPENDENT ENZYMES

A structural homology of the pyridoxal-5'-phosphate (PLP)-dependent en zyme serine hydroxymethyltransferase (SHMT) with aspartate aminotransf erase (AAT) is proposed. Although the two sequences are very dissimila r, a reasonable alignment was obtained using the profile analysis meth od. Sequences of AAT and dialkylglycine decarboxylase (DGD), for which crystal structure data are available, have been aligned on the basis of their structure superposition. A profile was then calculated and SH MT sequence aligned to it. Three of the four residues conserved in all aminotransferases (including the PLP-binding lysine) are matched. A p rofile search with DGD-AAT-SHMT profile is more selective and sensitiv e than individual sequence profiles for PLP-dependent enzyme detection . Potential homologies with the eryC1 gene product involved in erythro mycin biosynthesis and with amino acid decarboxylases were observed. H omology with AAT will be used as a guideline for planning site-directe d mutagenesis experiments on SHMT.