Type III secretion system flagellar brake protein YcgR (IPR023787)

Short name: T3SS_YcgR

Overlapping homologous superfamilies


Family relationships



This entry represents YcgR a member of the T3SS. It acts as a flagellar brake, regulating swimming and swarming in a bis-(3'-5') cyclic diguanylic acid (c-di-GMP)-dependent manner. Increasing levels of c-di-GMP lead to decreased motility. YcgR binds 1 c-di-GMP dimer per subunit.

YcgR is composed of two domains: an N-terminal domain of unknown function and a C-terminal PilZ domain. The PilZ domain binds c-di-GMP in vitro with an affinity that is high enough to allow it to respond to small changes in intracellular c-di-GMP levels. This domain organisation is conserved in a large number of proteobacteria. Therefore, the function of YcgR in motility control is likely to be conserved.

Higher concentrations of c-di-GMP in the presence of YcgR slows motor speed and inhibit chemotaxis by inhibiting ClockWise (CW) rotation. YcgR, when bound to c-di-GMP, interacts strongly with the flagellar motor proteins FliG and FliM. Interaction with FliG disrupts the organisation of the C-terminal domain altering the rotor-stator interface in a way that reduces the efficiency of torque generation and induces a CCW motor bias [PMID: 18034161].

GO terms

Biological Process

GO:0071945 regulation of bacterial-type flagellum-dependent cell motility by regulation of motor speed

Molecular Function

GO:0035438 cyclic-di-GMP binding

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.