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HapR has been recognized as a quorum-sensing master regulator in Vibrio cholerae. Because it controls a plethora of disparate cellular events, the absence of a functional HapR affects the physiology of V. cholerae to a great extent. In the current study, we pursued an understanding of an observation of a natural protease-deficient non-O1, non-O139 variant V. cholerae strain V2. Intriguingly, a nonfunctional HapR (henceforth designated as HapR V2 ) harboring a substitution of glycine to aspartate at position 39 of the N-terminal hinge region has been identified. An in vitro gel shift assay clearly suggested the inability of HapR V2 to interact with various cognate promoters. Reinstatement of glycine at position 39 restores DNA binding ability of HapR V2 (HapR V2G ), thereby rescuing the protease-negative phenotype of this strain. The elution profile of HapR V2 and HapR V2G proteins in size-exclusion chromatography and their circular dichroism spectra did not reflect any significant differences to explain the functional discrepancies between the two proteins. To gain insight into the structure-function relationship of these two proteins, we acquired small/wide angle x-ray scattering data from samples of the native and G39D mutant. Although Guinier analysis and indirect Fourier transformation of scattering indicated only a slight difference in the shape parameters, structure reconstruction using dummy amino acids concluded that although HapR adopts a "Y" shape similar to its crystal structure, the G39D mutation in hinge drastically altered the DNA binding domains by bringing them in close proximity. This altered spatial orientation of the helix-turn-helix domains in this natural variant provides the first structural evidence on the functional role of the hinge region in quorum sensing-related DNA-binding regulatory proteins of Vibrio spp.Studies on the quorum-sensing signal network of Vibrio cholerae have produced a rich harvest of data where the periodic appearance and performance of two regulatory proteins, namely LuxO and HapR, determine the fate of a plethora of disparate cellular events (1). Of these, HapR has been given the status of a master regulator because it controls a wide range of diverse physiological activities, thus exerting a profound influence on the survival and pathogenic potential of this bacterium. Collectively, it represses biofilm development and the production of primary virulence factors (2) while it stimulates the production of HA/protease (3), promotes chitin-induced competence (4), increases resistance to protozoan grazing (5), enhances the survival against oxidative stress (6), and controls the expression of the gene encoding Hcp (7). In a recent effort, Zhu and co-workers have elegantly characterized additional novel direct targets of HapR and illustrated two distinct binding motifs (motif 1 and motif 2) in all target promoters (8). Because it modulates a multitude of diverse cellular parameters, the absence of a functional HapR affects the physiology of V. cholerae to a great extent....

Transforming growth factor-β (TGF-β) is known to play a critical role in the pathogenesis of many progressive podocyte diseases. However, the molecular mechanisms regulating TGF-β signaling in podocytes remain unclear. Using a podocyte-specific Myo1c knockout, we demonstrate whether Myo1c is critical for TGF-β-signaling in podocyte disease pathogenesis. Specifically, podocyte-specific Myo1c knockout mice were resistant to fibrotic injury induced by Adriamycin or nephrotoxic serum. Further, loss of Myo1c also protected from injury in the TGFβ-dependent unilateral ureteral obstruction mouse model of renal interstitial fibrosis. Mechanistic analyses showed that loss of Myo1c significantly blunted TGF-β signaling through downregulation of canonical and non-canonical TGF-β pathways. Interestingly, nuclear rather than *

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