Protease susceptibility of the Caulobacter crescentus flagellar hook–basal body: a possible mechanism of flagellar ejection during cell differentiation

Abstract

When motile swarmer cells of Caulobacter crescentus differentiate into sessile stalked cells, the flagellum is ejected. To elucidate the molecular mechanism of the flagellar ejection, flagellar hook-basal body (HBB) complexes from C. crescentus were purified and characterized. The purified HBBs were less stable against acidic pH or protease treatment than HBBs of Salmonella typhimurium, supporting the view that flagellar ejection from C. crescentus is initiated by destruction of the fragile basal structures. In addition, protease treatment of the purified flagella resulted in the specific digestion of the MS ring complex, revealing for the first time the intact structure of the whole rod.

A Novel Gene Inactivation System Reveals Altered Periplasmic Flagellar Orientation in aBorrelia burgdorferi fliLMutant

“…Because of this stress, the mutant cells had a hook-filament-ejection phenotype (3). For C. crescentus, an fliL mutant was found to be paralyzed, and the FliL protein was reported to be required for the cell cycle-dependent ejection of the polar flagellum during the swimmer-to-stalk-cell transition (2,26,28,48). A P. mirabilis fliL mutant was reported to be nonmotile, failed to synthesize flagella, and had an elongatedcell phenotype (5).…”

“…However, B. burgdorferi motility and chemotaxis genes are not regulated by hierarchical gene regulatory cascades found in other species of bacteria, e.g., Escherichia coli (1,9,18,51). Genome sequence analysis also indicates that homologues of 28 and its antisigma factor FlgM are not present in B. burgdorferi and that all motility and chemotaxis genes identified to date appear to be transcribed by RNA polymerase containing 70 (9,20,51). Of at least 25 genes needed to build a functional bacterial flagellum, fliL is one of the genes that is not well understood.…”

Signals, Regulatory Networks, and Materials That Build and Break Bacterial Biofilms

“…In C. crescentus, a complex developmental program is associated with formation of the monolayer. The flagellum of cells destined for attachment is removed by a protease (3,157). In its place, a protrusion called a holdfast composed of oligomers of N-acetylglucosamine appears (150,296).…”

Getting in the Loop: Regulation of Development inCaulobacter crescentus

“…In the case of the flagellum, the filament, hook, and distal rod portions are detected in the culture supernatant as a single structure, suggesting that flagella are ejected (117,217,236). The mechanism of ejection is not known, but it may involve proteolytic degradation of part of the basal body complex.…”

“…FliF, a protein in the MS ring complex, is degraded at the swarmer 3 stalked cell transition, which may lead to flagellum release (108). Indeed, treatment of purified hook-basal body complexes with different proteases led to specific degradation of the MS ring and revealed intact rods (117). However, it should be noted that the rods revealed by proteolysis were full rods containing both the proximal and distal rod proteins, while rods attached to ejected flagella contain only the distal rod protein.…”