Comparative genomics of Helicobacter pylori: analysis of the outer membrane protein families

The two complete genomic sequences of Helicobacter pylori J99 and 26695 were used to compare the paralogous families (related genes within one genome, likely to have related function) of genes predicted to encode outer membrane proteins which were present in each strain. We identified five paralogous gene families ranging in size from 3 to 33 members; two of these families contained members specific for either H. pylori J99 or H. pylori 26695. Most orthologous protein pairs (equivalent genes between two genomes, same function) shared considerable identity between the two strains. The unusual set of outer membrane proteins and the specialized outer membrane may be a reflection of the adaptation of H. pylori to the unique gastric environment where it is found. One subfamily of proteins, which contains both channel-forming and adhesin molecules, is extremely highly related at the sequence level and has likely arisen due to ancestral gene duplication. In addition, the largest paralogous family contained two essentially identical pairs of genes in both strains. The presence and genomic organization of these two pairs of duplicated genes were analyzed in a panel of independent H. pylori isolates. While one pair was present in every strain examined, one allele of the other pair appeared partially deleted in several isolates.

A soluble deletion mutant of the human complement receptor type 1, which lacks the C4b binding site, is a selective inhibitor of the alternative complement pathway

The human complement receptor type 1 (CR1, CD35), is a single-chain glycoprotein consisting of 30 repeating homologous protein domains known as short consensus repeats (SCR) followed by transmembrane and cytoplasmic domains. The SCR themselves, considered in groups of seven, form long homologous repeats (LHR) which have been designated LHR-A, -B, -C, and -D for the most common human allotype of CR1. A soluble deletion mutant of CR1 which lacks the first seven N-terminal SCR (LHR-A) as well as the transmembrane and cytoplasmic domains was produced and characterized. The resulting protein, designated sCR1[desLHR-A], lacks the C4b binding site found in LHR-A, but retains the two C3b binding sites found in LHR-B and -C, respectively. The functional activities of sCR1[desLHR-A] were quantitatively compared in vitro to those of soluble complement receptor type 1 (sCR1) which has been shown to retain all known functions of the native cell surface receptor. sCR1[desLHR-A] and sCR1 competed equally for the binding of dimeric C3b to erythrocyte CR1. sCR1[desLHR-A] and sCR1 were similar in their capacity to serve as a cofactor in the factor I-mediated degradation of the C3b and C4b alpha chains. sCR1[desLHR-A] and sCR1 were comparable in their capacity to inhibit erythrocyte lysis and anaphylatoxin production mediated by the alternative complement pathway. sCR1[desLHR-A], however, was significantly less effective an inhibitor of erythrocyte lysis and anaphylatoxin production than sCR1 under conditions which allow classical pathway activation. These results demonstrate sCR1[desLHR-A] to be a selective inhibitor of the alternative complement pathway in vitro.