Nitric oxide-sensing H-NOX proteins govern bacterial communal behavior

•We describe how heme-nitric oxide/oxygen binding (H-NOX) domains function as sensors for nitric oxide (NO) in bacteria.•H-NOX proteins interact with bacterial signaling proteins in two-component signaling systems or in cyclic-di-GMP metabolism.•Structural and mechanistic studies have elucidated how H-NOX domains selectively bind NO and transduce ligand binding into function.•H-NOX proteins share a common role in reorganizing important bacterial communal behaviors in response to nitric oxide.•H-NOX pathways control motility, biofilm formation, quorum sensing, and symbiosis. Heme-nitric oxide/oxygen binding (H-NOX) domains function as sensors for the gaseous signaling agent nitric oxide (NO) in eukaryotes and bacteria. Mammalian NO signaling is well characterized and involves the H-NOX domain of soluble guanylate cyclase. In bacteria, H-NOX proteins interact with bacterial signaling proteins in two-component signaling systems or in cyclic-di-GMP metabolism. Characterization of several downstream signaling processes has shown that bacterial H-NOX proteins share a common role in controlling important bacterial communal behaviors in response to NO. The H-NOX pathways regulate motility, biofilm formation, quorum sensing, and symbiosis. Here, we review the latest structural and mechanistic studies that have elucidated how H-NOX domains selectively bind NO and transduce ligand binding into conformational changes that modulate activity of signaling partners. Furthermore, we summarize the recent advances in understanding the physiological function and biochemical details of the H-NOX signaling pathways.