Crystal structure of the antibiotic- and nitrite-responsive histidine kinase VbrK sensor domain from Vibrio rotiferianus.

Vibrio species are prevalent in the aquatic environments and can infect humans and aquatic organisms. Vibrio parahaemolyticus counteracts β-lactam antibiotics and enhances virulence using a regulation mechanism mediated by a two-component regulatory system (TCS) consisting of the VbrK histidine kinase and the VbrR response regulator. The periplasmic sensor domain of VbrK (VbrK) detects β-lactam antibiotics or undergoes S-nitrosylation in response to host nitrites. Although V. parahaemolyticus VbrK (vpVbrK) has recently been characterized through structural studies, it is unclear whether its structural features that are indispensable for biological functions are conserved in other VbrK orthologs. To structurally define the functionally critical regions of VbrK and address the structural dynamics of VbrK, we determined the crystal structures of Vibrio rotiferianus VbrK (vrVbrK) in two crystal forms and performed a comparative analysis of diverse VbrK structures. vrVbrK folds into a curved rod-shaped two-domain structure as observed in vpVbrK. The membrane-distal end of the vrVbrK structure, including the α3 helix and its neighboring loops, harbors both S-nitrosylation and antibiotic-sensing sites and displays high structural flexibility and diversity. Noticeably, the distal end is partially stabilized by a disulfide bond, which is formed by the cysteine residue that is S-nitrosylated in response to nitrite. Therefore, the distal end of VbrK plays a key role in initiating the VbrK-VbrR TCS pathway activation, and it is involved in the nitrosylation-mediated regulation of the structural dynamics of VbrK.