At least 12 Opa proteins are known and the many permutations of surface proteins make recognizing N. gonorrhoeae and mounting a defense by immune cells more difficult.Lipooligosaccharide (LOS) is a low-weight version of lipopolysaccharide present on the surfaces of most other Gram-negative bacteria. It is a sugar (saccharide) side chain attached to lipid A (thus "lipo-") in the outer membrane coating the cell wall of the bacteria. The root "oligo" refers to the fact that it is a few sugars shorter than the typical lipopolysaccharide. As an endotoxin, LOS provokes inflammation. The shedding of LOS by the bacteria is responsible for local injury in, for example, pelvic inflammatory disease. Although its main function is as an endotoxin, LOS may disguise itself with host sialic acid and block initiation of the complement cascade. Antigenic variation
N. gonorrhoeae evades the immune system through a process called antigenic variation. This process allows N. gonorrhoeae to recombine its genes and alter the antigenic determinants (sites where antibodies bind), such as the Type IV pili, that adorn its surface. Simply stated, the chemical composition of molecules is changed due to changes at the genetic level. N. gonorrhoeae is able to vary the composition of its pili, and LOS; of these, the pili exhibit the most antigenic variation due to chromosomal rearrangement. The PilS gene is an example of this ability to rearrange as its combination with the PilE gene is estimated to produce over 100 variants of the PilE protein.
The pili mediate adherence, movement, and DNA exchange. The Opa proteins interact with the immune system, as do the porins. Lipooligosaccharide (LOS) is an endotoxin that provokes an immune response. All are antigenic and all exhibit antigenic variation (see below). The pili exhibit the most variation. The pili, Opa proteins, porins, and even the LOS have mechanisms to inhibit the immune response, making asymptomatic infection possible.Dynamic polymeric protein filaments called type IV pili allow N. gonorrhoeae to adhere to and move along surfaces. To enter the host the bacteria uses the pili to adhere to and penetrate mucosal surfaces. The pili are a necessary virulence factor for N. gonorrhoeae; without them, the bacterium is unable to cause infection. To move, individual bacteria use their pili like a grappling hook: first, they are extended from the cell surface and attach to a substrate. Subsequent pilus retraction drags the cell forward. The resulting movement is referred to as twitching motility. N. gonorrhoeae is able to pull 100,000 times its own weight, and the pili used to do so are amongst the strongest biological motors known to date, exerting one nanonewton. The PilF and PilT ATPase proteins are responsible for powering the extension and retraction of the type IV pilus, respectively. The adhesive functions of the gonococcal pilus play a role in microcolony aggregation and biofilm formation. Surface proteins called Opa proteins can be used to bind to receptors on immune cells and prevent an immune response.