Penicillin-binding protein, transpeptidase <p>This signature identifies a large group of proteins, which include:</p><ul><li>Beta-lactamase precursor (<db_xref db="EC" dbkey="3.5.2.6"/>, penicillinase)</li><li>Peptidoglycan synthetase ftsI (<db_xref db="EC" dbkey="2.4.1.129"/>, peptidoglycan glycosyltransferase 3)</li><li>Methicillin resistance mecR1 protein</li><li>Methicillin resistance blaR1 protein</li></ul><p>The large number of penicillin binding proteins, which are represented in this group of sequences, are responsible for the final stages of peptidoglycan biosynthesis for cell wall formation. The proteins synthesise cross-linked peptidoglycan from lipid intermediates, and contain a penicillin-sensitive transpeptidase carboxy-terminal domain. The active site serine (residue 337 in <db_xref db="SWISSPROT" dbkey="P14677"/>) is conserved in all members of this family [<cite idref="PUB00003926"/>].</p><p>MecR1 and BlaR1 are metallopeptidases belonging to MEROPS peptidase family M56, clan M-. BlaR1 and MecR1 cleave their cognate transcriptional repressors BlaI and MecI, respectively, activating the synthesis of MecA.</p><p>MecR1 is present in <taxon tax_id="1280">Staphylococcus aureus</taxon> and <taxon tax_id="1296">Staphylococcus sciuri</taxon>, whereas BlaR1 (also known as BlaR, PenR1, or PenJ) has been found in <taxon tax_id="1402">Bacillus licheniformis</taxon>, <taxon tax_id="1282">Staphylococcus epidermidis</taxon>, <taxon tax_id="1283">Staphylococcus haemolyticus</taxon>, and several S. aureus strains. These proteins are either plasmid-encoded, chromosomal, or transposon-mediated. MecR1/BlaR1 proteins are made up by homologous N-terminal 330-residue transmembrane metallopeptidase domains linked to extracellular 260-residue homologous PBP-like penicillin sensor moieties. </p>