Pathogenic Neisseria spp. possess a repertoire of phase-variable Opacity proteins that mediate various pathogen--host cell interactions [2]. These proteins are integral membrane proteins related to other porins.

1: Opacity genes in Neisseria gonorrhoeae: control of phase and antigenic variation. Stern A, Brown M, Nickel P, Meyer TF; Cell 1986;47:61-71. PMID:3093085

2: The role of neisserial Opa proteins in interactions with host cells. Dehio C, Gray-Owen SD, Meyer TF; Trends Microbiol 1998;6:489-495. PMID:10036728