Crystal structure of the lytic CHAPK domain of the endolysin LysK from Staphylococcus aureus bacteriophage K

Virology Journal

Mark J van Raaij³  Aidan Coffey²  Carmela Garcia-Doval¹  Ruth Keary²  Marta Sanz-Gaitero³ 

[1] Current address: Department of Biochemistry, University of Zurich, Zurich, Switzerland;Department of Biological Sciences, Cork Institute of Technology, Bishopstown, Cork, Ireland;Departamento de Estructura de Macromoleculas, Centro Nacional de Biotecnologia (CNB–CSIC), Calle Darwin 3, E-28049 Madrid, Spain

关键词: Zinc;    Staphylococcus;    Protease;    Peptidoglycan;    Endolysin;    Crystallography;    Calcium;    Bacteriophage;   

Others  :  1148770
DOI  :  10.1186/1743-422X-11-133

 received in 2014-04-28, accepted in 2014-07-04,  发布年份 2014

【 摘 要 】

Background

Bacteriophages encode endolysins to lyse their host cell and allow escape of their progeny. Endolysins are also active against Gram-positive bacteria when applied from the outside and are thus attractive anti-bacterial agents. LysK, an endolysin from staphylococcal phage K, contains an N-terminal cysteine-histidine dependent amido-hydrolase/peptidase domain (CHAP_K), a central amidase domain and a C-terminal SH3b cell wall-binding domain. CHAP_K cleaves bacterial peptidoglycan between the tetra-peptide stem and the penta-glycine bridge.

Methods

The CHAP_K domain of LysK was crystallized and high-resolution diffraction data was collected both from a native protein crystal and a methylmercury chloride derivatized crystal. The anomalous signal contained in the derivative data allowed the location of heavy atom sites and phase determination. The resulting structures were completed, refined and analyzed. The presence of calcium and zinc ions in the structure was confirmed by X-ray fluorescence emission spectroscopy. Zymogram analysis was performed on the enzyme and selected site-directed mutants.

Results

The structure of CHAP_K revealed a papain-like topology with a hydrophobic cleft, where the catalytic triad is located. Ordered buffer molecules present in this groove may mimic the peptidoglycan substrate. When compared to previously solved CHAP domains, CHAP_K contains an additional lobe in its N-terminal domain, with a structural calcium ion, coordinated by residues Asp45, Asp47, Tyr49, His51 and Asp56. The presence of a zinc ion in the active site was also apparent, coordinated by the catalytic residue Cys54 and a possible substrate analogue. Site-directed mutagenesis was used to demonstrate that residues involved in calcium binding and of the proposed active site were important for enzyme activity.

Conclusions

The high-resolution structure of the CHAP_K domain of LysK was determined, suggesting the location of the active site, the substrate-binding groove and revealing the presence of a structurally important calcium ion. A zinc ion was found more loosely bound. Based on the structure, we propose a possible reaction mechanism. Future studies will be aimed at co-crystallizing CHAP_K with substrate analogues and elucidating its role in the complete LysK protein. This, in turn, may lead to the design of site-directed mutants with altered activity or substrate specificity.

【 授权许可】

   
2014 Sanz-Gaitero et al.; licensee BioMed Central Ltd.

【 图 表 】

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