AUTHOR=Gao Rongsui , Li Defeng , Lin Yuan , Lin Jingxia , Xia Xiaoyun , Wang Hui , Bi Lijun , Zhu Jun , Hassan Bachar , Wang Shihua , Feng Youjun 

TITLE=Structural and Functional Characterization of the FadR Regulatory Protein from Vibrio alginolyticus

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=7

YEAR=2017

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2017.00513

DOI=10.3389/fcimb.2017.00513

ISSN=2235-2988

ABSTRACT=<p>The structure of <italic>Vibrio cholerae</italic> FadR (VcFadR) complexed with the ligand oleoyl-CoA suggests an additional ligand-binding site. However, the fatty acid metabolism and its regulation is poorly addressed in <italic>Vibrio alginolyticus</italic>, a species closely-related to <italic>V. cholerae</italic>. Here, we show crystal structures of <italic>V. alginolyticus</italic> FadR (ValFadR) alone and its complex with the palmitoyl-CoA, a long-chain fatty acyl ligand different from the oleoyl-CoA occupied by VcFadR. Structural comparison indicates that both VcFadR and ValFadR consistently have an additional ligand-binding site (called site 2), which leads to more dramatic conformational-change of DNA-binding domain than that of the <italic>E. coli</italic> FadR (EcFadR). Isothermal titration calorimetry (ITC) analyses defines that the ligand-binding pattern of ValFadR (2:1) is distinct from that of EcFadR (1:1). Together with surface plasmon resonance (SPR), electrophoresis mobility shift assay (EMSA) demonstrates that ValFadR binds <italic>fabA</italic>, an important gene of unsaturated fatty acid (UFA) synthesis. The removal of <italic>fadR</italic> from <italic>V. cholerae</italic> attenuates <italic>fabA</italic> transcription and results in the unbalance of UFA/SFA incorporated into membrane phospholipids. Genetic complementation of the mutant version of <italic>fadR</italic> (Δ42, 136-177) lacking site 2 cannot restore the defective phenotypes of Δ<italic>fadR</italic> while the wild-type <italic>fadR</italic> gene and addition of exogenous oleate can restore them. Mice experiments reveals that VcFadR and its site 2 have roles in bacterial colonizing. Together, the results might represent an additional example that illustrates the <italic>Vibrio</italic> FadR-mediated lipid regulation and its role in pathogenesis.</p>