This family includes the Haemophilus influenzae opacity-associated protein. This protein is required for efficient nasopharyngeal mucosal colonisation, and its expression is associated with a distinctive transparent colony phenotype. OapA is thought to be a secreted protein, and its expression exhibits high-frequency phase variation [1,2]. This motif occurs at the N-terminus of these proteins. It contains a conserved histidine followed by a run of hydrophobic residues.

1: Identification and characterization of a cell envelope protein of Haemophilus influenzae contributing to phase variation in colony opacity and nasopharyngeal colonization. Weiser JN, Chong ST, Greenberg D, Fong W; Mol Microbiol 1995;17:555-564. PMID:8559074

2: Phenotypic switching of Haemophilus influenzae. Moxon ER, Gewurz BE, Richards JC, Inzana T, Jennings MP, Hood DW; Mol Microbiol 1996;19:1149-1150. PMID:8830271