Members of this family are homologs to the surface protein A (NspA) from Neisseria meningitidis, which is a promising vaccine candidate. NspA is a highly conserved membrane protein that elicits protective antibody responses in mice against Neisseria meningitidis infection. NspA forms an 8-stranded antiparallel ß-barrel, whereas the four loops at the extracellular side of the NspA molecule form a long cleft, which contains mainly hydrophobic residues and harbors a detergent molecule, suggesting that the protein might function in the binding of hydrophobic ligands, such as lipids. Loops 2 and 3, are more important regarding antibody binding.

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