Characterization of the opa (class 5) gene family of Neisseria meningitidis

Abstract

Class 5 outer membrane proteins of Neisseria meningitidis show both phase- and antigenic variation of expression. The proteins are encoded by a family of opa genes that share a conserved framework interspersed with three variable regions, designated the semivariable (SV) region and hypervariable regions 1 (HV₁) and 2 (HV₂). In this study, we determined the number and DNA sequence of all of the opa genes of meningococcal strain FAM18, to assess the structural and antigenic variability in the family of proteins made by one strain. Pulsed field electrophoresis and Southern blotting showed that there are four opa genes in the FAM18 chromosome, and that they are not tightly clustered. DNA sequence analysis of the four cloned genes showed a modest degree of diversity in the SV region and more extensive differences in the HV₁ and HV₂ regions. There were four versions of HV₁ and three versions of HV₂ among the four genes. Each of the FAM18 opa loci contained a gene with a unique combination of SV, HV₁, and HV₂ sequences. We used λgt11 cloning and synthetic peptides to demonstrate that HV₂ sequences completely encode the epitopes for two monoclonal antibodies specific for different class 5 proteins of FAM18.