Similarity between the 38-kilodalton lipoprotein of Treponema pallidum and the glucose/galactose-binding (MglB) protein of Escherichia coli

Abstract

The recent discovery that abundant and immunogenic lipoproteins constitute the integral membrane proteins of Treponema pallidum has prompted efforts to investigate their importance in the physiology and ultrastructure of the organism and in immune responses during infection. Earlier studies identified a 38-kDa lipoprotein of T. pallidum believed to be specific to the pathogen. In the present study, monoclonal antibodies generated against the 38-kDa lipoprotein of T. pallidum reacted with cognate 37-kDa molecules in the nonpathogens Treponema phagedenis, Treponema denticola, and Treponema refringens. Cloning and expression of the 38-kDa-lipoprotein gene of T. pallidum in Escherichia coli revealed that the recombinant product displayed a slightly larger (39-kDa) apparent molecular mass but remained reactive with anti-38-kDa-protein monoclonal antibodies. The recombinant product was processed and acylated in E. coli. DNA and amino acid sequence analyses indicated an open reading frame encoding 403 amino acids, with the first 25 amino acids corresponding to a leader peptide terminated by a signal peptidase II processing site of Val-Val-Gly-Cys. The predicted mature protein is 378 amino acids in length with a deduced molecular weight of 40,422 (excluding acylation). Southern blotting failed to demonstrate in nonpathogenic treponemes genomic sequences homologous with the 38-kDa-lipoprotein gene of T. pallidum. Computer analysis revealed that the 38-kDa lipoprotein of T. pallidum had 34.2% identity and 58.9% similarity with the glucose/galactose-binding protein (MglB) of E. coli and Salmonella typhimurium. Furthermore, of the 19 amino acids of MglB involved in carbohydrate binding, the 38-kDa lipoprotein had identity with 11. These studies have allowed the first putative functional assignment (carbohydrate binding) to a T. pallidum integral membrane protein. Recognition of this potential physiological role for the 38-kDa lipoprotein underscores the possibility that the membrane biology of T. pallidum may more closely resemble that of gram-positive organisms, which also utilize lipoproteins as anchored transporters, than that of gram-negative bacteria to which T. pallidum often is analogized.

Evidence for a methyl-accepting chemotaxis protein gene (mcp1) that encodes a putative sensory transducer in virulent Treponema pallidum

“…Although a general consensus motif based upon known E. coli and B. subtilis methylation sites was utilized as the basis for such assignments (18,67), the three sites do not precisely match the consensus; the assignments of these methylation sites thus remain putative until more precise information can be obtained. Interestingly, by inference from other studies (4,17), it is predicted that CheR and CheB, which are involved in the methylation and demethylation of MCPs (67,68), exist in T. pallidum. If so, treponemal CheR and CheB may exhibit specificity for methylation and demethylation of Mcp1 somewhat divergent from the known specificities displayed by E. coli and B. subtilis CheR and CheB (67,68).…”

“…This sequence also appears in the C termini of the four known E. coli MCPs, with the exception of a single amino acid substitution (NAAVEAA) (7). To minimize unnecessary degeneracy, codon preferences for T. pallidum (1,4,28,52,70,76) were taken into account in the design of MCP-2.…”

“…The inability to cultivate T. pallidum in vitro and the consequent lack of a genetic exchange system for analysis of the organism continue to impede progress in elucidating the molecular biology and virulence traits of this important human pathogen (48,60,61). Given these experimental constraints, the acquisition of new information about T. pallidum ultrastructure, physiology, and membrane biology remains the principal means of advancing our conceptual understanding of treponemal pathogenesis (4,20,51,53,63,77).…”

“…Initial insight into possible T. pallidum sensory transduction mechanisms was engendered in the discovery of a 38-kDa lipoprotein of T. pallidum as a homolog of Escherichia coli MglB (4). In E. coli and other enteric bacteria, MglB is a periplasmic, high-affinity receptor for glucose (and galactose) and a component of an ATP-binding cassette operon involved in glucose/galactose import (27,43).…”

Evidence for in vivo but not in vitro expression of a Borrelia burgdorferi outer surface protein F (OspF) homologue

“…Except for the N-terminal residue, there were no other cysteines in the mature polypeptide. Typicat of other spirochaetal lipoproteins (Akins et al, 1993;Becker et al, 1994;Bergstrom et aL, 1989;Lam et aL, 1994;Fuchs et aL, 1992;Norris et aL, 1992;Hsu etal., 1989), hydrophilicity analysis revealed that the mature polypeptide was hydrophilic and did not contain large stretches of hydrophobic residues consistent with transmembrane domains (data not shown).…”