A Single-Domain FlgJ Contributes to Flagellar Hook and Filament Formation in the Lyme Disease Spirochete Borrelia burgdorferi

Abstract

T he bacterial flagellum is a sophisticated macromolecular complex. Its structure and assembly have been well studied in two model organisms, Escherichia coli and Salmonella enterica serovar Typhimurium (for reviews, see references 5, 13, 36, and 58). The flagellum is composed of at least 25 different proteins that can be grouped into three physical parts: the basal body, the flagellar hook, and the filament. The basal body is imbedded within the cell envelope and works as a reversible rotary motor; the flagellar hook and filament extend outwards to the cell exterior and function as a universal joint and a propeller, respectively. The basal body is very complex and consists of several functional units: the membranesupramembrane (MS)-C ring (rotor), the rod (driveshaft), the L-P rings (bushings), the stator (torque generator), and the flagellar export apparatus. The motor is driven by an inward-directed electrochemical gradient of protons or sodium. The torque generated by the motor is mechanically transmitted to the filament via the rod-hook complex, leading to the rotation of flagellar filament, which propels the bacterial cells forward.Flagellar assembly is a sequential process (for reviews, see references 1 and 13). It begins with the MS ring assembly. Built onto the MS ring is a hollow rod that spans the periplasmic space. After formation of the MS ring/rod complex, the FlgI and FlgH proteins assemble around the rod to form the P and L rings, respectively. The hook and filament proteins are subsequently assembled on the rod. The flagellar rod begins with the MS ring and stops at the flagellar hook. Thus, it needs to penetrate the peptidoglycan (PG) layer during flagellar formation. It has been postulated that FlgJ is essential for flagellar rod formation (25,45), with the N-terminal domain (rod-capping) acting as a scaffold for rod assembly and the C-terminal domain functioning as a PG hydrolase (PGase), which makes a hole in the PG layer to allow rod penetration. In S. Typhimurium, flgJ null mutants are aflagellated and nonmotile, while mutants that do not express the PGase domain produce fewer flagella and show poor motility (25, 45). However, the PGase domain is absent in the FlgJ homologs from several bacterial phyla, including Alphaproteobacteria, Deltaproteobacteria, and Epsilonproteobacteria and Spirochaetes (44). As there is only one domain, these homologs are referred to as "single-domain FlgJ." The function of these FlgJ homologs remains unknown.Spirochetes are a group of motile bacteria that have a unique morphology and are able to swim in highly viscous gel-like environments (for reviews, see references 11 and 31). It is believed that motility plays a critical role in the biology of spirochetes and in the processes of diseases caused by pathogenic spirochetes (9,11,16,32,55). Spirochetes swim by means of two rotating bundles of periplasmic flagella (PFs) that reside between the outer membrane and cell cylinder (23,32,38,49). PFs are structurally similar to the flagella of other bacteria, as each ...

The C Terminus of the Flagellar Muramidase SltF Modulates the Interaction with FlgJ in Rhodobacter sphaeroides

“…We have previously reported that FlgJ from Rhodobacter sphaeroides lacks the muramidase domain (11). At least three studies have been performed that analyzed FlgJ homologues from various bacteria, and it was noticed that various alphaproteobacteria, including R. sphaeroides, possess FlgJ homologues that lack the C-terminal muramidase domain (8,25,39). In R. sphaeroides, FlgJ is similar to the N-terminal part of FlgJ from Salmonella enterica, suggesting that this polypeptide of 100 residues accomplishes the same function as the N-terminal domain of FlgJ from S. enterica, which acts as a scaffolding rod-capping protein (11,13).…”

Motility Is Crucial for the Infectious Life Cycle of Borrelia burgdorferi

“…The flagella that reside between the outer membrane and cell cylinder form an elegant ribbon in the periplasmic space as they wrap around the cell cylinder (18)(19)(20)(21)(22)(23)(24). A single periplasmic flagellum is composed of a motor (FliF and many other proteins), hook (FlgE), and filament (FlaB and FlaA) (25)(26)(27). B. burgdorferi flagellar filaments consist of a major FlaB and a minor FlaA protein comprising 10 to 14% and less than 0.5% of total cellular protein, respectively (28,29).…”

Hypothetical Protein BB0569 Is Essential for Chemotaxis of the Lyme Disease Spirochete Borrelia burgdorferi

“…(B to D) Determination of the stability of BB0569 in the wild type (B) and the ⌬mcp 2 (C) and ⌬mcp 3 (D) mutants. The assay was carried out as previously described (38). Translation of B. burgdorferi was arrested by adding spectinomycin (100 g/ml) to the cultures.…”

“…Immunoblots were developed with the horseradish peroxidase-labeled secondary antibodies by using the Pierce ECL Western blotting substrate kit (Thermo Scientific, Rockford, IL). Densitometry of immunoreactive proteins in the blots was used to determine the relative amounts of proteins, as previously described (38). Densitometry was measured by using the Molecular Imager ChemiDoc XRS imaging system (Bio-Rad, Hercules, CA).…”

“…A protein turnover assay was carried out as previously described (37,38). Briefly, B. burgdorferi strains were grown in BSK-II medium at 34°C.…”