Polypeptide composition of Chlamydia trachomatis

Strains of Chlamydia trachomatis representative of 14 serotypes were grown in HeLa 229 cells. HeLa cell susceptibility to chlamydial infection was increased by treating the host cells with DEAE-dextran. Optimal conditions of DEAE-dextran treatment were determined for each serotype of C. trachomatis to maximize chlamydial yields. Chlamydial polypeptides were selectively radiolabelled with 3H-labelled amino acids in the presence of emetine, an inhibitor of HeLa cell protein synthesis. The radiolabelled chlamydiae were purified from host cell components by density gradient centrifugation and their polypeptide composition was determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The distribution of the major chlamydial polypeptide of 38 000 to 42 000 daltons amongst the different serotypes correlated closely with the predominant human infections caused by each serotype. Lymphogranuloma venereum agents possessed a unique polypeptide of 118 000 daltons not found amongst trachoma inclusion conjunctivitis strains of chlamydiae. Chlamydial surface polypeptides were selectively radiolabelled with 125I by lactoperoxidase-catalysed oxidation. The major chlamydial polypeptide and polypeptides of 155 000 and 29 000 daltons were thus identified as surface polypeptides of the chlamydial elementary body. It is suggested that the 155 000 dalton polypeptide is a species-specific antigen, the major polypeptide is the principal outer membrane protein, and the 29 000 dalton polypeptide is the type-specific antigen.