Salmonella typhimurium mutants defective in flagellar filament regrowth and sequence similarity of FliI to F0F1, vacuolar, and archaebacterial ATPase subunits

flhF, a Bacillus subtilis flagellar gene that encodes a putative GTP-binding protein

We describe the sequence and characterization of the Bacillus subtilis flhF gene. flhF encodes a basic polypeptide of 41 kDa that contains a putative GTP-binding motif. The sequence of FlhF reveals a structural relationship to two Escherichia coli proteins, Ffh and FtsY, as well as to other members of the SRP54 family, in a domain presumed to bind GTP. flhF is located in a large operon consisting of chemotaxis and flagellar genes. Cells deficient in flhF are nonmotile. Through the use of anti-flagellar antibodies we have established that flhF is a flagellar (fla) gene. Thus, flhF is a unique flagellar gene in that it encodes a GTP-binding protein with similarities to members of the SRP54 family of proteins. These data suggest that flagellar biosynthesis in B. subtilis requires GTP.

Evolution of structure and function of V-ATPases

Proton pumping ATPases/ATPsynthases are found in all groups of present-day organisms. The structure of V- and F-type ATPases/ATP synthases is very conserved throughout evolution. Sequence analysis shows that the V- and F-type ATPases evolved from the same enzyme already present in the last common ancestor of all known extant life forms. The catalytic and noncatalytic subunits found in the dissociable head groups of the V/F-type ATPases are paralogous subunits, i.e., these two types of subunits evolved from a common ancestral gene. The gene duplication giving rise to these two genes (i.e., encoding the catalytic and noncatalytic subunits) predates the time of the last common ancestor. Mapping of gene duplication events that occurred in the evolution of the proteolipid, the noncatalytic and the catalytic subunits, onto the tree of life leads to a prediction for the likely subunit structure of the encoded ATPases. A correlation between structure and function of V/F-ATPases has been established for present-day organisms. Implications resulting from this correlation for the bioenergetics operative in proto-eukaryotes and in the last common ancestor are presented. The similarities of the V/F-ATPase subunits to an ATPase-like protein that was implicated to play a role in flagellar assembly are evaluated. Different V-ATPase isoforms have been detected in some higher eukaryotes. These data are analyzed with respect to the possible function of the different isoforms (tissue specific, organelle specific) and with respect to the point in their evolution when these gene duplications giving rise to the isoforms had occurred, i.e., how far these isoforms are distributed.

Morphological pathway of flagellar assembly in Salmonella typhimurium

The process of flagellar assembly was investigated in Salmonella typhimurium. Seven types of flagellar precursors produced by various flagellar mutants were purified by CsCl density gradient protocol. They were characterized morphologically by electron microscopy, and biochemically by two-dimensional gel electrophoresis. The MS ring is formed in the absence of any other flagellar components, including the switch complex and the putative export apparatus. Four proteins previously identified as rod components, FlgB, FlgC, FlgF, FlgG, and another protein, FliE, assemble co-operatively into a stable structure. The hook is formed in two distinct steps; formation of its proximal part and elongation. Proximal part formation occurs, but elongation does not occur, in the absence of the LP ring. FlgD is necessary for hook formation, but not for LP-ring formation. A revised pathway of flagellar assembly is proposed based on these and other results.

Molecular and functional characterization of the Salmonella invasion gene invA: homology of InvA to members of a new protein family

One of the earliest steps in the pathogenic cycle of the facultative intracellular pathogen Salmonella spp. is the invasion of the cells of the intestinal epithelium. We have previously identified a genetic locus, inv, that allows Salmonella spp. to enter cultured epithelial cells. invA is a member of this locus, and it is the first gene of an operon consisting of at least two additional invasion genes. We have constructed strains carrying nonpolar mutations in invA and examined the individual contribution of this gene to the invasion phenotype of Salmonella typhimurium. Nonpolar S. typhimurium invA mutants were deficient in invasion of cultured epithelial cells although they were fully capable of attaching to the same cells. In addition, unlike wild-type S. typhimurium, invA mutants did not alter the normal architecture of the microvilli of polarized epithelial cells nor did they cause any alterations in the distribution of actin microfilaments of infected cells. The invasion phenotype of invA mutants was readily rescued by wild-type S. typhimurium when cultured epithelial cells were simultaneously infected with both strains. On the contrary, in a similar experiment, the adherent Escherichia coli strain RDEC-1 was not internalized into cultured cells when coinfected with wild-type S. typhimurium. The invA locus was found to be located at about 59 min on the Salmonella chromosome, 7% linked to mutS. The nucleotide sequence of invA showed an open reading frame capable of encoding a polypeptide of 686 amino acids with eight possible membrane-spanning regions and a predicted molecular weight of 75,974. A protein of this size was visualized when invA was expressed in a bacteriophage T7 RNA polymerase-based expression system. The predicted sequence of InvA was found to be homologous to Caulobacter crescentus FlbF, Yersinia LcrD, Shigella flexneri VirH, and E. coli FlhA proteins. These proteins may form part of a family of proteins with a common function, quite possibly the translocation of specific proteins across the bacterial cell membrane.

Characterization of the fliE genes of Escherichia coli and Salmonella typhimurium and identification of the FliE protein as a component of the flagellar hook-basal body complex

Within flagellar region III of Escherichia coli and Salmonella typhimurium, the genomic organization has been largely established. An exception is fliE, a gene whose exact location and product function are not well understood. We cloned the fliE gene, obtained its DNA sequence, and identified its product.fliE was found to be a monocistronic transcriptional unit, adjacent to and divergent from the large fliF operon. It is several kilobases distant from the nearest flagellar operon in the other direction, the fliD operon, and constitutes the first operon within the newly defined region IIIb, which contains the genes fliE through fliR.fliE encodes a small, moderately hydrophilic protein with a deduced molecular mass of 11,114 Da (E. coli) or 11,065 Da (S. typhimurium). We identified a protein within the isolated hook-basal body complex as the fliE gene product on the basis of its size and comparison of its N-terminal amino acid sequence with that deduced from the gene sequence. From gel electrophoresis and autoradiography of 35S-labeled S. typhimurium hook-basal body complexes (C.J. Jones, R.M. Macnab, H. Okino, and S.-I. Aizawa, J. Mol. Biol. 212:377-387, 1990) and the deduced number of sulfur-containing residues in FliE, we estimated the stoichiometry of the protein in the hook-basal body complex to be about nine subunits. FliE does not undergo cleavage of a signal peptide, nor does it show any sequence similarity to the axial components like the rod or hook proteins, which are believed to be exported by the flagellum-specific export pathway. On the basis of this and other evidence, we suggest that FliE may be in the vicinity of the MS ring, perhaps acting as an adaptor protein between the ring and rod substructures.

Surface presentation of Shigella flexneri invasion plasmid antigens requires the products of the spa locus

An avirulent, invasion plasmid insertion mutant of Shigella flexneri 5 (pHS1059) was restored to the virulence phenotype by transformation with a partial HindIII library of the wild-type invasion plasmid constructed in pBR322. Western immunoblot analysis of pHS1059 whole-cell lysates revealed that the synthesis of the invasion plasmid antigens VirG, IpaA, IpaB, IpaC, and IpaD was similar to that seen in the corresponding isogenic S. flexneri 5 virulent strain, M90T. IpaB and IpaC, however, were not present on the surface of pHS1059 as was found in M90T, suggesting that the transport or presentation of the IpaB and IpaC proteins onto the bacterial surface was defective in the mutant. pHS1059 was complemented by pWR266, which carried contiguous 1.2- and 4.1-kb HindIII fragments of the invasion plasmid. pHS1059(pWR266) cells were positive in the HeLa cell invasion assay as well as colony immunoblot and enzyme-linked immunosorbent assays, using monoclonal antibodies to IpaB and IpaC. These studies established that the antigens were expressed on the surface of the transformed bacteria. In addition, water extraction of pHS1059 and pHS1059(pWR266) whole cells, which can be used to remove IpaB and IpaC antigens from the surface of wild-type M90T bacteria, yielded significant amounts of these antigens from pHS1059(pWR266) but not from pHS1059. Minicell and DNA sequence analysis indicated that several proteins were encoded by pWR266, comprising the spa loci, which were mapped to a region approximately 18 kb upstream of the ipaBCDAR gene cluster. Subcloning and deletion analysis revealed that more than one protein was involved in complementing the Spa- phenotype in pHS1059. One of these proteins, Spa47, showed striking homology to ORF4 of the Bacillus subtilis flaA locus and the fliI gene sequence of Salmonella typhimurium, both of which bear strong resemblance to the alpha and beta subunits of bacterial, mitochondrial, and chloroplast proton-translocating F0F1 ATPases.

The cell cycle-regulated flagellar gene flbF of Caulobacter crescentus is homologous to a virulence locus (lcrD) of Yersinia pestis

We have characterized flbF, a key locus located at the top of the flagellar gene hierarchy of Caulobacter crescentus. This gene is required for transcription from sigma 54 promoters of fla genes expressed late in the cell cycle. We have determined the nucleotide sequence of the gene, mapped the 5' end of the flbF RNA, and examined the pattern of expression in the cell cycle. Our results show that flbF is expressed earlier in the cell cycle than other fla genes, that it is expressed at a low level throughout the stalked cell cycle, and that its 5' regulatory region contains sequences that can be aligned with the sigma 28 promoter consensus reported for enteric bacteria. flbF contains an open reading frame of 700 residues with an amino-terminal half rich in hydrophobic residues that could correspond to six to eight transmembrane domains. The translated flbF sequence is very similar to LcrD (low calcium response) encoded by virulence plasmids of pathogenic Yersinia spp. (G. Plano, S. Barve, and S. Straley, J. Bacteriol. 173:7293-7303, 1991). LcrD and FlbF can be aligned over the entire length of the proteins with the greatest degree of sequence identity (45%) in the hydrophobic amino-terminal region. The high degree of sequence homology of proteins derived from widely differing organisms, including Caulobacter and Yersinia species, suggests that FlbF and LcrD may be representatives of a larger family of regulatory proteins with a common sensor mechanism for modifying responses to appropriate stimuli.

Properties of the Bacillus subtilis chemotaxis protein CheF, a homolog of the Salmonella typhimurium flagellar protein FliJ

The nucleotide sequence of Bacillus subtilis cheF was corrected. It encodes an 18-kDa protein that is homologous to FliJ, a protein required for formation of basal bodies in Escherichia coli and Salmonella typhimurium. Methanol release is abnormal in cheF mutants, suggesting that the morphology and functioning of the motor affects methanol formation.

The flaA locus of Bacillus subtilis is part of a large operon coding for flagellar structures, motility functions, and an ATPase-like polypeptide

We cloned and sequenced 8.3 kb of Bacillus subtilis DNA corresponding to the flaA locus involved in flagellar biosynthesis, motility, and chemotaxis. The DNA sequence revealed the presence of 10 complete and 2 incomplete open reading frames. Comparison of the deduced amino acid sequences to data banks showed similarities of nine of the deduced products to a number of proteins of Escherichia coli and Salmonella typhimurium for which a role in flagellar functioning has been directly demonstrated. In particular, the sequence data suggest that the flaA operon codes for the M-ring protein, components of the motor switch, and the distal part of the basal-body rod. The gene order is remarkably similar to that described for region III of the enterobacterial flagellar regulon. One of the open reading frames was translated into a protein with 48% amino acid identity to S. typhimurium FliI and 29% identity to the beta subunit of E. coli ATP synthase.