| Type: | Family | Name: | Signal transduction response regulator, modified HD-GYP domain-containing, putative |
| Description: | Two-component signal transduction systems enable bacteria to sense, respond, and adapt to a wide range of environments, stressors, and growth conditions []. Some bacteria can contain up to as many as 200 two-component systems that need tight regulation to prevent unwanted cross-talk []. These pathways have been adapted to response to a wide variety of stimuli, including nutrients, cellular redox state, changes in osmolarity, quorum signals, antibiotics, and more []. Two-component systems are comprised of a sensor histidine kinase (HK) and its cognate response regulator (RR) []. The HK catalyses its own auto-phosphorylation followed by the transfer of the phosphoryl group to the receiver domain on RR; phosphorylation of the RR usually activates an attached output domain, which can then effect changes in cellular physiology, often by regulating gene expression. Some HK are bifunctional, catalysing both the phosphorylation and dephosphorylation of their cognate RR. The input stimuli can regulate either the kinase or phosphatase activity of the bifunctional HK.A variant of the two-component system is the phospho-relay system. Here a hybrid HK auto-phosphorylates and then transfers the phosphoryl group to an internal receiver domain, rather than to a separate RR protein. The phosphoryl group is then shuttled to histidine phosphotransferase (HPT) and subsequently to a terminal RR, which can evoke the desired response [, ].This entry represents a group of signal transduction response regulators which contain a modified version of the HD-GYP domain as an output domain.Response regulators of the microbial two-component signal transduction systems typically consist of an N-terminal CheY-like receiver (phosphoacceptor) domain and a C-terminal output (usually DNA-binding) domain. In response to an environmental stimulus, a phosphoryl group is transferred from the His residue of sensor histidine kinase to an Asp residue in the CheY-like receiver domain of the cognate response regulator [, , ]. Phosphorylation of the receiver domain induces conformational changes that activate an associated output domain, which in turn triggers the response. Phosphorylation-induced conformational changes in response regulator molecule have been demonstrated in direct structural studies []. For more information on the receiver domain, please see .HD-GYP is a conserved domain found in response regulator modules of various signal transduction systems. The involvement of the HD-GYP domain in signal transduction was originally proposed on the basis of its association with CheY-like and other signal transduction domains [] and was later directly demonstrated experimentally by showing that RpfG is involved in regulation of the biosynthesis of extracellular endoglucanase and polysaccharide [].A modification of the HD-GYP domain, which is found in this group, , , and several smaller groups, lacks the conserved distal portion of the domain and has certain substitutions in the characteristic metal-binding residues [] of the HD superfamily phosphohydrolases, which likely render it catalytically inactive. Note that the prototypical HD domain () is not recognised in many members of this group.The exact mode of action and targets of the HD-GYP output domain are not known []. HD-GYP proteins are associated to the HD domain superfamily of metal-dependent phosphohydrolases; HD designates the principal conserved residues implicated in metal binding and catalysis []. The version of the HD-type domain present in members of (and in some other groups) has many additional highly conserved residues, including a conserved GYP motif, and is therefore called HD-GYP [, ].It has been noted that the highly conserved sequence of the HD-GYP domain suggests high substrate specificity []. On the basis of its association with the GGDEF diguanylate cyclase domain, it has been also predicted that the HD-GYP domain may be involved in the metabolism of cyclic diguanylate or in dephosphorylation of some phosphotransfer domain []. | Short Name: | Sig_transdc_resp-reg_put |
