title: Structural insights into the broad substrate specificity of carboxypeptidase T from Thermoactinomyces vulgaris.
abstract: The crystal structures of carboxypeptidase T (CpT) complexes with phenylalanine and arginine substrate analogs - benzylsuccinic acid and (2-guanidinoethylmercapto)succinic acid - were determined by the molecular replacement method at resolutions of 1.57 Å and 1.62 Å to clarify the broad substrate specificity profile of the enzyme. The conservative Leu211 and Leu254 residues (also present in both carboxypeptidase A and carboxypeptidase B) were shown to be structural determinants for recognition of hydrophobic substrates, whereas Asp263 was for recognition of positively charged substrates. Mutations of these determinants modify the substrate profile: the CpT variant Leu211Gln acquires carboxypeptidase B-like properties, and the CpT variant Asp263Asn the carboxypeptidase A-like selectivity. The Pro248-Asp258 loop interacting with Leu254 and Tyr255 was shown to be responsible for recognition of the substrate's C-terminal residue. Substrate binding at the S1' subsite leads to the ligand-dependent shift of this loop, and Leu254 side chain movement induces the conformation rearrangement of the Glu277 residue crucial for catalysis. This is a novel insight into the substrate selectivity of metallocarboxypeptidases that demonstrates the importance of interactions between the S1' subsite and the catalytic center.
authors.affiliation: State Research Institute for Genetics and Selection of Industrial Microorganisms, Moscow, Russia.
authors.forename: Valery Kh
authors.initials: VKh
authors.lastname: Akparov
authors.forename: Vladimir I
authors.initials: VI
authors.lastname: Timofeev
authors.forename: Ilyas G
authors.initials: IG
authors.lastname: Khaliullin
authors.forename: Vytas
authors.initials: V
authors.lastname: Švedas
authors.forename: Galina G
authors.initials: GG
authors.lastname: Chestukhina
authors.forename: Inna P
authors.initials: IP
authors.lastname: Kuranova
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D002268:Carboxypeptidases / Q000737:chemistry*; D002384:Catalysis; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D011485:Protein Binding; D013379:Substrate Specificity; D013386:Succinates / Q000737:chemistry; D056509:Thermoactinomyces / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; D013386:Succinates; C000249:benzylsuccinic acid; D002268:Carboxypeptidases; C076614:CPT protein, Thermoactinomyces vulgaris
keywords: (2-guanidinoethylmercapto)succinic acid; X-ray analysis; benzylsuccinic acid; carboxypeptidase T; substrate specificity