Aeromonas salmonicida possesses two genes encoding homologs of the major outer membrane protein, OmpA

Abstract

Two homologs of the outer membrane protein OmpA were identified in Aeromonas salmonicida by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoblotting, and amino-terminal sequence analyses. An A. salmonicida genomic DNA library was constructed by using GEM-11 and recombinant phage carrying both genes (ompAI and ompAII) selected by immunoscreening. A 5.0-kb BamHI fragment containing the two genes in tandem was subcloned in pBluescript and used for further subcloning and sequencing of the genes. The encoded proteins (M r ‫؍‬ 33,564 and 32,536 for mature OmpAI and OmpAII, respectively) had only 64% identity with each other and otherwise had the highest level of homology to OmpA proteins from the members of the family Enterobacteriaceae. Based on the Escherichia coli OmpA model, an eight-stranded amphipathic ␤-barrel model for the membrane assembly of the N-terminal half of OmpAI and OmpAII was predicted. Most variation between the two proteins was localized to the predicted surface loops and periplasmic turns, while the transmembrane strands and C-terminal domains were highly conserved. Expression of ompAI and ompAII separately in E. coli indicated that both genes could be independently transcribed from their own promoters and that both gene products were assembled into the E. coli outer membrane. A survey of different Aeromonas spp. by PCR revealed that possession of two tandem ompA genes was widespread among this genus. This is the first report of any bacterial species possessing two genes for homologs of this major outer membrane protein.The OmpA protein was initially identified as one of the major proteins of the outer membrane of Escherichia coli. Either a closely related homolog of this protein or a more distantly related relative has now been identified as a major protein of the outer membrane of a wide range of gramnegative bacteria (5,12,15,16,27). Major physiological functions attributed to the OmpA family include maintenance of the structural integrity and morphology of the cell (33) and porin activity (35), as well as a role in conjugation and bacteriophage binding (26). A role in bacterial virulence has been implicated for some of these proteins (9,30,37). The importance of the OmpA family of proteins has been further strengthened by the recent observation that amino acid (aa) sequence homology extends to certain proteins from grampositive bacteria as well as lipoproteins from gram-negative bacteria, all with the common property of interacting with peptidoglycan (10).In all cases thus far examined, cloning of the ompA (or ompA-like) gene has identified a single gene which appears to be constitutively expressed. The structure and assembly of the E. coli protein have been studied in detail. Current models (31,36) propose that E. coli OmpA is assembled into the outer membrane with a bidomain structure: an N-terminal membrane domain (residues 1 to 170), comprising an eight-transmembrane-stranded amphipathic ␤-barrel, and a C-terminal periplasmic domain (residues 171 to 325). The relative res...

Evaluation of an Isogenic Major Outer Membrane Protein-Deficient Mutant in the Human Model of Haemophilus ducreyi Infection

“…Their tandem arrangement on the chromosome may be due to a gene duplication event. Only one other bacterium, Aeromonas salmonicida, has been reported to express two OmpA-like proteins (8).…”

Sequence Diversity and Molecular Evolution of the Heat-Modifiable Outer Membrane Protein Gene ( ompA ) of Mannheimia ( Pasteurella ) haemolytica , Mannheimia glucosida , and Pasteurella trehalosi

“…on May 7, 2018 by guest http://jb.asm.org/ expected because similar findings have been described for Aeromonas salmonicida and Haemophilus ducreyi (8,29). The presence of putative ribosome-binding, promoter, and termination sequences associated with each of the ompA genes also provides indirect evidence that they are independently transcribed (8,54).…”

“…It also seems likely that a common underlying mechanism is responsible for generating tandem ompA genes in certain bacterial species and that the expression of two OmpA homologs provides a selective advantage to these organisms. It has been suggested that the two ompA genes of A. salmonicida and H. ducreyi have arisen by gene duplication (8,29). Based on the relatively low level of homology between the two OmpA proteins of A. salmonicida, Costello et al (8) concluded that such a gene duplication event occurred in the distant evolutionary past.…”

“…The presence of putative ribosome-binding, promoter, and termination sequences associated with each of the ompA genes also provides indirect evidence that they are independently transcribed (8,54). A retrospective examination of the OMP profiles of a wide range of P. trehalosi isolates (16) indicated that the expression of two OmpA homologs is common in this species.…”

Identification of the major outer membrane proteins of Aeromonas salmonicida

“…To date, other than the S-layer, a limited number of Aeromonas salmonicida OMPs have been identified. Costello and co-workers reported that A. salmonicida expresses 2 OmpA porin family gene products (OmpAI and OmpAII) coded for by 2 distinct genes (Costello et al 1996). Other A. salmonicida surface proteins identified include a maltose-inducible LamB homolog (Dodsworth et al 1993), the ExeD protein of the general secretion pathway used to translocate extracellular proteins from the periplasmic space across the outer membrane (Karlyshev & MacIntyre 1995), a 43 and a 28 kDa OMP involved in pore-forming activity (Darveau et al 1983, Lutwyche et al 1995.…”