The expression and characterization of a putative adhesin B from H. influenzae

In the H. influenzae type b (Hib) genome, two putative adhesin B genes, HI0119 and HI0362, have been identified on the basis of homology to the adhesin B (FimA) of Streptococcus parasanguis. We expressed and characterized one of them, HI0119, from a non-typeable H. influenzae strain (NTHI). This 37 kDa protein was selectively isolated from an H. influenzae surface protein (water) extract by elution from a celite matrix with EDTA. The adhesin B protein is 97.7% identical to that of H. influenzae, strain Rd, has 23.7% identity and 47.8% similarity to FimA of Streptococcus parasanguis but is distinguished from the FimA family by the absence of the N-terminal lipid anchor consensus sequence LXXC, the presence of a C-terminal disulfide-bonded domain, and a central histidine-rich domain. Recombinant fusion protein bound specifically to celite. Antisera raised against fusion protein recognized a 37 kDa protein from whole cell extracts of H. influenzae on Western blots. A truncated mutant lacking the C-terminal disulfide-bonded domain and a Cys308 to Ser mutant were constructed and expressed as fusion proteins. Both mutants retained celite binding. However, purified fusion proteins could not, unlike H. influenzae, bind Hep2 cells, suggesting that HI0119 may not be an adhesin in this organism.