Identification of aMoraxella catarrhalisOuter Membrane Protein Exhibiting Both Adhesin and Lipolytic Activities

Abstract

The UspA1 and Hag proteins have previously been shown to be involved in the ability of the Moraxella catarrhalis wild-type strain O35E to bind to human Chang and A549 cells, respectively. In an effort to identify novel adhesins, we generated a plasmid library of M. catarrhalis DNA fragments, which was introduced into a nonadherent Escherichia coli strain. Recombinant E. coli bacteria were subsequently enriched for clones that gained the ability to bind to Chang and A549 cells, yielding the plasmid pELFOS190. The unencapsulated, gram-negative bacterium Moraxella catarrhalis is one of the leading causes of otitis media in young children and of lower respiratory tract infections in adults with chronic obstructive pulmonary disease (COPD). In developed countries, more than 80% of children under the age of 3 years will be diagnosed at least once with otitis media, and M. catarrhalis is responsible for 15 to 25% of all of these cases (6, 7, 10, 12, 26-29, 41, 51, 60). Lower respiratory tract infections (exacerbations) have been shown to contribute to the progression of COPD, and of the approximately 20 million cases of exacerbations documented each year in the United States, up to 35% result from M. catarrhalis infections (3,41,43,54,55).A vaccine that provides protection against M. catarrhalis is highly desirable due to this substantial morbidity as well as the growing concern over antibiotic resistance observed in clinical isolates (30). Toward this end, current research is focused on the identification of potential antigens with emphasis on the outer membrane proteins (OMPs) (26,34,35). While M. catarrhalis OMPs with a wide variety of functions have been identified, adhesins are particularly attractive vaccine candidates because they are surface-exposed antigens. Furthermore, adhesins generally play a crucial role in colonization and pathogenesis. For many bacteria, adherence to epithelial surfaces contributes to the evasion of host clearance mechanisms (4,25,59). Previous studies with M. catarrhalis have identified UspA1 (32, 36), UspA2 (2, 8, 36), Hag (14,15,17,19,24,45,47; M. M. Holm and E. R. Lafontaine, unpublished data), lipooligosaccharide (24), OMPCD (49), and UspA2H (32) as potential adhesins. Of these, only UspA1 and UspA2H have been directly shown to mediate adherence to human cells (32,36). However, while UspA1 is expressed by virtually all strains tested to date, only ϳ20% of clinical isolates contain an uspA2H gene (32, 37).The present study describes the identification of the novel M. catarrhalis OMP McaP. While this protein was identified based on its ability to function as an adhesin, we report that it also displays the enzymatic activity of an esterase and a phospholipase B (PLB). MATERIALS AND METHODSStrains, plasmids, tissue culture (TC) cell lines, and growth conditions. The bacterial strains and plasmids described in this study are listed in Table 1. M. catarrhalis was routinely cultured at 37°C on Todd-Hewitt medium (Difco). When cultured on agar plates, M. catarrhalis was incubated in an at...

Molecular Aspects ofMoraxella catarrhalisPathogenesis

“…Adhesion studies using uspA1 and hag knockout mutants indicated the presence of another adherence factor. Indeed, a gain-of-function (adhesion) approach using a nonadherent Escherichia coli strain led to the identification of a novel adhesin that exhibited both phospholipase B and esterase activities (145). This 62-kDa OMP, named McaP, was classified as a conventional autotransporter protein containing a 12-␤-barrel translocator domain and an N-terminal passenger domain that harbors both adhesion and lipolytic activity (Fig.…”

Moraxella catarrhalis induces ERK- and NF- B-dependent COX-2 and prostaglandin E2 in lung epithelium

“…It is reported herein, that COX-2 expression and PGE 2 release was dependent on UspA1 of M. catarrhalis. UspA1, an important adhesin, mediating the adherence of M. catarrhalis to human respiratory epithelial cells, has been described as being present on the surface of most M. catarrhalis disease isolates examined to date [6,9,22,28]. UspA1 is known to adhere to the epithelial cell-associated laminin and fibronectin [9].…”

Temporal development of the humoral immune response to surface antigens of Moraxella catarrhalis in young infants

“…These 9 recombinant proteins (from 7 different OMPs) represented the majority of published M. catarrhalis immunogenic proteins discovered at the time that the study was initiated, and are derived from the reference M. ) [16,20,22,26]. Orf238 and orf296 are hypothetical proteins that share homology with lipoprotein family A proteins and with the M. osloensis disulfide isomerase gene, which encodes a virulence factor, respectively.…”