These genes were found to be constitutively expressed in three strains of C. perfringens that were isolated from cases of gas gangrene in humans. Both recombinant proteins expressed from these genes, rFbpA and rFbpB, have been shown to bind to Fn in a ligand blotting assay when rFbp are immobilized on either a PVDF membrane or a plastic microplate (20). In the present study, the Fn epitope recognized by rFbp was determined. Further, the characteristics of serum Fn which has been bound by rFbp were analyzed. To generate His-tagged rFbpA and rFbpB proteins the C. perfringens strain 13 genes fbpA and fbpB were first amplified by PCR

as described previously (20). The resultant DNA fragments were cloned into Tyrosine Kinase Inhibitor Library the pET16-b vector (Merck KGaA,

Darmstadt, Germany) and transformed into the E. coli BL21-CodonPlus (DE3) RIL strain. The transformants were grown at 37°C in Luria-Bertani broth (Invitrogen, Carlsbad, CA, USA) containing 100 μg/ml ampicillin and 34 μg/ml chloramphenicol to an optical density of 0.6 at 600 nm. Induction of gene expression was accomplished with 1 mM IPTG for 3 hr at 37°C. After incubation, the cells were harvested, and were lysed in a French press (10 000 pounds per square inch). His-tagged proteins were purified on a Ni2+-Sepharose column. Fn was purified from pooled human serum using a gelatin-Sepharose column. Fn was obtained by Dinaciclib elution with 4 M urea in 5 mM VBS, pH 7.4. Human Fn proteolytic N-terminal 70-kDa and human Fn proteolytic N-terminal 30-kDa fibrin/heparin binding, 4-Aminobutyrate aminotransferase human Fn proteolytic 45-kDa gelatin binding and recombinant human III1-C (7 kDa) fragments were purchased from Sigma (St. Louis, MO, USA). The 110-kDa Fn fragment (type III2–10) was obtained by digestion of Fn with thermolysin, followed by gel-filtration on a HiLoad 16/60 Superdex 200 column (GE Healthcare, Little Chalfont,

UK) as described by Borsi et al. (21). The anti-Fn mAbs HB91 and HB39, obtained from their respective mAb-producing hybridomas, were purchased from ATCC (Manassas, VA, USA). The anti-Fn mAbs ZET1 and ZET2 were obtained from hybridomas established by us as follows: SP-2/0 myeloma cells were hybridized with spleen cells from BALB/c mice immunized with Fn (ZET1), an 80-kDa Fn fragment containing Fn type III3–11 (ZET2). Each mAb (IgG1) was purified from the hybridoma culture supernatant using a protein G column. All plate binding assays were carried out by individually coating the wells of an EIA/RIA plate (Corning, NY, USA) with 50 μl protein solution at a concentration of 0.02 mg/ml in 10 mM BB, (pH 8.5), for 30 min at room temperature. The wells were then blocked by incubation for 1 hr at room temperature with 250 μl of 1% (w/v) BSA in BB. Following three washes with 20 mM PBST (pH 7.4), the binding of biotinylated proteins or specific antibodies was tested by addition of 100 μl of a 0.