The Substrate-free and -bound Crystal Structures of the Duplicated Taurocyamine Kinase from the Human Parasite Schistosoma mansoni

• Published in: The Journal of biological chemistry 2015-05, Vol.290 (20), p.12951-12963
• Main Authors: Merceron, Romain, Awama, Ayman M., Montserret, Roland, Marcillat, Olivier, Gouet, Patrice
• Format: Article
• Language: English
• Subjects: Animals; Crystallography, X-Ray; Helminth Proteins - chemistry; Humans; isothermal titration calorimetry (ITC); Models, Molecular; Phosphotransferases (Nitrogenous Group Acceptor) - chemistry; Protein Structure and Folding; Protein Structure, Secondary; Protein Structure, Tertiary; Schistosoma mansoni; Schistosoma mansoni - enzymology; small angle x-ray scattering (SAXS); substrate specificity; Taurine - analogs & derivatives; Taurine - chemistry; taurocyamine kinase; transition state; x-ray crystallography
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M114.628909

The taurocyamine kinase from the blood fluke Schistosoma mansoni (SmTK) belongs to the phosphagen kinase (PK) family and catalyzes the reversible Mg2+-dependent transfer of a phosphoryl group between ATP and taurocyamine. SmTK is derived from gene duplication, as are all known trematode TKs. Our crystallographic study of SmTK reveals the first atomic structure of both a TK and a PK with a bilobal structure. The two unliganded lobes present a canonical open conformation and interact via their respective C- and N-terminal domains at a helix-mediated interface. This spatial arrangement differs from that observed in true dimeric PKs, in which both N-terminal domains make contact. Our structures of SmTK complexed with taurocyamine or l-arginine compounds explain the mechanism by which an arginine residue of the phosphagen specificity loop is crucial for substrate specificity. An SmTK crystal was soaked with the dead end transition state analog (TSA) components taurocyamine-NO32−-MgADP. One SmTK monomer was observed with two bound TSAs and an asymmetric conformation, with the first lobe semiclosed and the second closed. However, isothermal titration calorimetry and enzyme kinetics experiments showed that the two lobes function independently. A small angle x-ray scattering model of SmTK-TSA in solution with two closed active sites was generated. Trematode taurocyamine kinases are contiguous dimers of unknown structure. The first reported crystal structure of taurocyamine kinase displays an original bilobal arrangement compared with true dimeric phosphagen kinases. Each lobe is capable of enzymatic activity and substrate binding in a non-mutually exclusive manner. This structure can serve as a tool for the rational design of anti-schistosomiasis drugs.