Gonococcal pili. Primary structure and receptor binding domain.

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Abstract
The complete amino acid sequence of pilin from gonococcal strain MS11 and the sequence of constant and variable regions from strain R10 pilin were determined to elucidate the structural basis for adherence function, antigenic diversity and polymeric structure. The MS11 pilin sequence consisted of159 amino acids in a single polypeptide chain with 2 cysteines in disulfide linkage and serine-bonded PO43- residues. TC-2 (31-111), a soluble monomeric pilus peptide prepared by arginine-specific digestion, bound human endocervical, but not buccal or HeLa [cervical carcinoma] cells and therefore is postulated to encompass the receptor binding domain. Variable regions of CNBr-3 (CNBr fragment 3) appeared to confer antigenic diversity and comprised segments in which changes in the position of charged residues occured in hydrophilic, .beta. turns. Residues 2-21 and 202-221 of gonococcal pilins and lower eurkaryotic actins, respectively, exhibited 50% homology. When these residues were arranged at intervals of 100 degrees of arc on helical wheels, the identical amino acids comprised a hydrophobic face on 1 side of the helix. This observation, the hydrophobic character of this region and the tendency for TC-1 (residues 1-30) to aggregate in H2O suggest that this stretch interacts with ohter subunits to stabilize polymeric structure.