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
Human crude and recombinant interleukin 1 (IL-1) was found to dose- and time-dependently affect the biosynthesis of (pro)insulin in isolated rat islets of Langerhans. Incubation of rat islets with either 0.5 U/ml or 5 U/ml of crude IL-1 for 1 h had no detectable effect on (pro)insulin biosynthesis. After 24 hours of exposure 0.5 U/ml of crude or 0.6 ng/ml of recombinant IL-1 (beta) increased the (pro)insulin biosynthesis by 42% and 58%, respectively, whereas a 10-fold greater concentration of IL-1 decreased the (pro)insulin biosynthesis by 74% and 89%, respectively. The increase in (pro)insulin biosynthesis was accompanied by an increase in total protein biosynthesis indicating a nonspecific stimulatory action of low IL-1 concentrations. In contrast, high IL-1 concentrations caused a more selective decrease of the (pro) insulin biosynthesis when compared to the total protein biosynthesis. In addition, low IL-1 concentrations were found to increase and high concentrations to decrease the relative levels of pre-proinsulin mRNA suggesting that IL-1 may act both at a pre- and post-translational level of insulin biosynthesis.
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