sctC

sctC is a gene encoding the secretin protein SctC, a core component of the bacterial type III secretion system (T3SS). It codes for an outer membrane protein that forms part of the secretin ring, a multimeric channel in the outer membrane through which effector proteins are secreted into host cells. SctC is typically found in pathogenic Gram-negative bacteria and is essential for the assembly and function of the T3SS basal body.

Functionally, SctC assembles into a multimeric complex that spans the outer membrane, creating the outer membrane ring of the T3SS. This ring collaborates with inner membrane components such as SctD and SctJ to form the basal structure that anchors the secretion apparatus and enables translocation of effectors and translocators. Disruption of sctC often impairs secretion and virulence, underscoring its critical role in T3SS activity.

In terms of homologs and naming, many bacteria use the sctC designation for the secretin subunit. In Salmonella enterica serovar Typhimurium, the functional homolog is InvG, while in Yersinia species it is YscC. SctC proteins are commonly located within type III secretion gene clusters or pathogenicity islands and are often encoded alongside other sct genes involved in the assembly and operation of the T3SS.

Structure and biogenesis are characteristic of bacterial secretins: SctC proteins are typically large, with periplasmic and outer membrane-spanning regions and an ability to form a multimeric ring. In some systems, assembly into the outer membrane may require auxiliary factors or pilotin-like proteins to assist correct localization and integration.

Significance: SctC is a key virulence determinant in many pathogens and represents a potential target for strategies aimed at inhibiting T3SS-dependent delivery of bacterial effectors.