Opa proteins of gonocci are located in the outer membrane and play a very important role in infection. Opa proteins cause adherence to specific cells, like macrophages and epithelial cells, and are required for the uptake of these gonococci into the eukaryotic cells (thus avoiding the immune system)
"Why can't we just make antibodies to the Opa proteins?"
Phase Variation
Phase Variation: Of all the 11 Opa genes, only a few are expressed. Expression of a single Opa gene is also dependent on genetic variation. Sequencing the leader sequence (the part of the protein that facilities exit from the cell) gives the DNA nucleotide sequence CTCTT that is repeated up to nine times.
And, as you know from your molecular biology, this one sequence can code for different amino acids, depending on the position of the start codon.
Depending on the different permutation, CTCTT will give the amino acids Leucine, Phenylalanine, or Serine, based on the orientation of the reading frame.
While the actual amino acids in the leader sequence are not too important what is important is the codon following the CTCTT repeat. The CCG (Serine) must by in frame to allow synthesis of a leader peptide Opa's export to the surface of the bacteria.
So, the codon will be in frame for
all multimers of CTCTT which are divisible by three.
For example:
| CTCTT|CTCTT|CTCTT|CTCTT|CTCTT| CGG will not give a correct reading frame to read the serine -BUT- |CTCTT|CTCTT|CTCTT| CCG will give the correct reading frame for the serine amino acid
|
So the continual variation of which Opa proteins (remember, there are 11 total) are displayed in a given gonococcal population allow the bacteria to confuse the immune system and cause a chronic infection.