eLife assessment
This study presents a potentially valuable investigation of water coordination in a specific kinase family with a focus on the regulation of osmosensing protein kinases. X-ray crystallographic approaches combined with functional assays are used to address the hypothesis that bound water participates in the osmosensing mechanism as an allosteric kinase inhibitor. Evidence for changes in kinase conformation and space group of the crystal as a function of added low molecular weight polyethylene glycol is solid, but there alternative interpretations for much of the other data cannot be excluded and the work thus remains incomplete. With stronger evidence and/or alternative explanations explored, the work would be of considerable interest to the kinase field as well as colleagues studying allosteric regulation of protein function.