Function of Neisserial Outer Membrane Phospholipase A in Autolysis and Assessment of Its Vaccine Potential

Abstract

Outer membrane phospholipase A (OMPLA) is an outer membrane-localized enzyme, present in many gram-negative bacterial species. It is implicated in the virulence of several pathogens. Here, we investigated the presence, function, and vaccine potential of OMPLA in the human pathogen Neisseria meningitidis. Immunoblot analysis showed the presence of OMPLA in 28 out of 33 meningococcal strains investigated. The OMPLAnegative strains all contained a pldA gene, but these alleles contained premature stop codons. All six Neisseria gonorrhoeae strains tested, but only two out of seven commensal neisserial strains investigated, expressed OMPLA, showing that OMPLA is expressed by, but not limited to, many pathogenic neisserial strains. The function of OMPLA was investigated by assessing the phenotypes of isogenic strains, expressing no OMPLA, expressing wild-type levels of OMPLA, or overexpressing OMPLA. OMPLA exhibited phospholipase activity against endogenous phospholipids. Furthermore, OMPLA was characterized as an autolysin that acted under specific conditions, such as prolonged growth of the bacteria. The vaccine potential of the protein was investigated by immunizing mice with in vitro refolded, recombinant OMPLA. High levels of antibody titers were obtained, but the murine sera were neither bactericidal nor protective. Also, convalescent patients and vaccinee sera did not contain detectable levels of anti-OMPLA antibodies, indicating that OMPLA may not be sufficiently immunogenic to be included in a meningococcal vaccine.

Quantitative Proteomics of the Neisseria Gonorrhoeae Cell Envelope and Membrane Vesicles for the Discovery of Potential Therapeutic Targets

“…Moreover, our experiments revealed ubiquitous expression of a number of recognized proteins including an outer membrane-localized enzyme, Phospholipase A, and a surface-exposed lipoprotein Ng-MIP (Table II). Concurring with our data, these proteins were found invariably expressed in many different GC and meningococcal isolates (78,79). Perhaps not surprisingly, proteins participating in the process of outer membrane biogenesis, BamA (Omp85) and BamD (ComL), were identified by iTRAQ experiments as equally present in GC strains (Table II).…”

Functional and Specific Antibody Responses in Adult Volunteers in New Zealand Who Were Given One of Two Different Meningococcal Serogroup B Outer Membrane Vesicle Vaccines

“…This antigen was present in roughly equal amounts in both vaccines, but the FetA in MeNZB had a slightly lower molecular weight in polyacrylamide gels, consistent with a deletion in the main variable immunogenic region of this protein compared with the FetA in MenBvac (49,53). Although outer membrane phospholipase A is present in strain 44/76 and was identified in OMVs from NZ98/254 (8,57), no IgG reaction was observed with this protein expressed in OMVs from a PorA-negative 44/76 strain, in support of the findings of a recent study (8).…”

AmiC Functions as an N -Acetylmuramyl- l -Alanine Amidase Necessaryfor Cell Separation and Can Promote Autolysis in Neisseria gonorrhoeae

“…Thus, lysis occurring in our amiC mutant aggregates may be a direct effect of outer membrane instability resulting from the unusual cell architecture. It is known that autolysis can be triggered by membrane instability, and it was recently shown that N. gonorrhoeae mutants deficient in phospholipase A are decreased in autolysis (4). Alternatively, the absence of AmiC may allow another peptidoglycanase to act in an uncontrolled manner, leading to autolysis.…”