Anthranilate synthase subunit organization in Chromobacterium violaceum

ABSTRACT. Tryptophan is an aromatic amino acid used for protein synthesis and cellular growth. Chromobacterium violaceum ATCC 12472 uses two tryptophan molecules to synthesize violacein, a secondary me-tabolite of pharmacological interest. The genome analysis of this bacteri-um revealed that the genes trpA-F and pabA-B encode the enzymes of the tryptophan pathway in which the first reaction is the conversion of choris-mate to anthranilate by anthranilate synthase (AS), an enzyme complex. In the present study, the organization and structure of AS protein subunits from C. violaceum were analyzed using bioinformatics tools available on the Web. We showed by calculating molecular masses that AS in C. violaceum is composed of α (TrpE) and β (PabA) subunits. This is in agreement with values determined experimentally. Catalytic and regula-tory sites of the AS subunits were identified. The TrpE and PabA subunits contribute to the catalytic site while the TrpE subunit is involved in the allosteric site. Protein models for the TrpE and PabA subunits were built by restraint-based homology modeling using AS enzyme, chains A and B, from Salmonella typhimurium (PDB ID 1I1Q)