Ultrastructural and biochemical studies of a recombinant Treponema pallidum surface antigen designated 4D have been conducted due to its likely biological significance. Electron microscopy demonstrated that the 190-kilodalton (kDa) 4D molecule is an ordered ring structure of 10-nm diameter. The 90-kDa proteinase K-treated 4D is an ordered ring structure of 6-nm diameter. Evidence is presented that the 190-kDa ordered ring is maintained by noncovalent bonds; 19-kDa monomers can reassociate in vitro to reform a 190-kDa molecule. Amino acid composition analysis of 190-kDa 4D showed that the molecule is composed of 45% hydrophobic residues. Evidence relating the structure of the 4D ordered ring to its potential role in the pathogenesis of syphilis is discussed.
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Fehniger et al. (1986) studied this question.
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