Protein L, a bacterial immunoglobulin-binding protein and possible virulence determinant

Abstract

Protein L, an immunoglobulin kappa light chain-binding protein, is expressed on the surfaces of certain strains of Peptostreptococcus magnus. Thirty strains of P. magnus were isolated from clinical specimens, and four of them were found to express protein L. Among the 30 strains, 7 were isolated from the vaginas of patients with bacterial vaginosis, and the 4 immunoglobulin-binding strains all belonged to this group, results demonstrating that expression of protein L is correlated to peptostreptococcal virulence (P < 0.001 in the chi-square test) and indicating that the molecule could be a virulence determinant. Similar amounts of protein L were expressed by the four strains, and when protein L was isolated from three of them and analyzed in Western blots, the same immunoglobulin-binding patterns were obtained. The N-terminal amino acid sequences of tryptic fragments of protein L were determined, and on the basis of these sequence data, oligonucleotides were synthesized and used to screen a genomic library of peptostreptococcal DNA in the lambda ZAP vector. The nucleotide sequence was determined for one of the clones detected in this way. In dot blots and Southern blots of peptostreptococcal DNA, another synthetic oligonucleotide probe based on this sequence showed no hybridization with DNA samples from the nonexpressing strains, whereas similar Southern blot patterns were seen when DNA samples from protein L-expressing strains were analyzed. These results suggest that the protein L gene is missing rather than being down regulated in protein L-negative strains of P. magnus. Finally, the probe did not hybridize with DNA purified from immunoglobulin-binding streptococcal and staphylococcal strains or with Escherichia coli DNA, suggesting that the protein L gene is unique to protein L-expressing strains of P. magnus. this novel kind of immunoglobulin-binding bacterial protein could be a virulence determinant of P. magnus. MATERIALS AND METHODSBacteria. Thirty strains of the anaerobic species P. magnus were isolated from clinical specimens received at the

Isolation and characterization of transposon Tn4001-generated, cytadherence-deficient transformants of Mycoplasma pneumoniae and Mycoplasma genitalium

“…However, our search showed that pMG032 (77~kDa protein) shared significant homology with the protein products derived from M. geni-t&urn ORFs MG096 and MG288 [15] and with the L protein of Peptostreptococcus magnus [32,33]. In the TIGR database MG096 is listed as a heretofore unknown sequence whereas MG288 is homologous to P. mugnus L protein.…”

“…Interestingly, the L protein of P. magnus, like mycoplasma adhesins, contains several repe,ats followed by a proline-rich COOH terminus. The L protein binds to immunoglobulin kappa light chains (Ig,), and its preferential expression in the P. magnus strains isolated from patients with bacterial vaginosis, implicates this protein as a virulence determinant [32,33].…”

Whole-body autoradiography reveals that the Peptostreptococcus magnus immunoglobulin-binding domains of protein L preferentially target B lymphocytes in the spleen and lymph nodes in vivo

“…Although in vitro studies have shown that protein L can trigger release of inflammatory cytokines by mast cells and basophils (Patella et al, 1990;Genovese et al, 2003), whether protein L has a pathogenic effect on B lymphocytes or other cells is not yet known. Considering the in vivo targeting of protein L described here, it is noteworthy that, although protein L is a surface-associated molecule, substantial amounts of the protein are released from the bacterial surface (Kastern et al, 1990). However, the pathogenic consequences of cellular targeting by protein L in vivo remain to be established.…”

“…Approximately 10% of clinical isolates of P. magnus carry and express the gene encoding protein L, and the majority of these isolates are from patients with gynaecological infections. This suggests a role for protein L in the virulence of P. magnus (Kastern et al ., 1990).…”

Identification of molecular mechanisms used by Finegoldia magna to penetrate and colonize human skin

“…The superantigen, protein L, is a surface protein with high affinity for immunoglobulin light chains and can induce the release of pro-inflammatory mediators (Björck, 1988;Genovese et al, 2003). Protein L is expressed by approximately 10% of F. magna isolates and is known to be associated with bacterial vaginoses (Kastern et al, 1990). Another surface protein that could promote virulence, is the albumin binding protein PAB, which was found to give the expressing strain a significant increase in growth rate (de Château and Björck, 1994;de Château et al, 1996).…”