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. Author manuscript; available in PMC: 2022 Jun 1.
Published in final edited form as: Curr Opin Microbiol. 2021 Feb 26;61:8–15. doi: 10.1016/j.mib.2021.01.004

Figure 2.

Figure 2.

The diversity of PAS domain roles in bacterial proteins. All cartoons show the bacterial cytoplasmic membrane and the dimeric form of each protein. (a) PAS as a signal sensor as illustrated by VqmA from Vibrio cholerae. VqmA-PAS binds to the autoinducer 3,5-dimethyl-pyrazine-2-ol (DPO) and signals to a helix-turn-helix (HTH) DNA-binding domain to regulate transcription [7,8]. (b) PAS as a signal modulator as illustrated by Aer2 from V. cholerae. PAS1 modulates the extent of O2-mediated signaling from PAS2, which sends a conformational signal through two HAMP domains and a kinase control module (KCM) [15]. The KCM regulates a series of downstream chemosensory proteins. (c) PAS as a signal transducer as illustrated by BvgS from Bordetella bronchiseptica. BvgS transduces signals from a periplasmic Venus fly-trap (VFT) domain via a cytoplasmic PAS domain to C-terminal histidine kinase (HK; comprised of DHp and CA subdomains), response regulator (Rec), and histidine phosphotransfer (Hpt) domains, thus regulating kinase and phosphatase functions [16]. (d) PAS as a dimerization motif as illustrated by DgcE from Escherichia coli. The three DgcE PAS domains are essential for protein dimerization, which activates DgcE’s GGDEF (diguanylate cyclase) domain to produce c-di-GMP, and overcomes the anti-oligomerizing effect of the EAL (phosphodiesterase) domain [18]. PAS dimerization occurs after a protein complex binds to the membrane-associated sensor (MASE1) domain of DgcE. The EAL domain is degenerate and does not degrade c-di-GMP to guanosine monophosphate (GMP). (e) PAS as a protein interaction motif as illustrated by CetA and CetB from Camplyobacter jejuni. CetA and CetB constitute a bipartite energy-taxis system with the domains of the aerotaxis receptor, Aer, divided between two proteins. CetB is a PAS domain that is predicted to bind FAD, sense redox, and transmit signals through interaction with the HAMP domain of CetA [19]. (f) PAS as a cellular localization determinant as illustrated by CckA from Caulobacter crescentus. PAS-A directs CckA to either cell pole, whereas PAS-B targets CckA to new cell poles [20]. PAS-A and PAS-B also have sensory roles that regulate CckA’s kinase (HK; comprised of DHp and CA subdomains) and phosphatase (Rec) functions.