Structural analysis of chlamydial major outer membrane proteins.

The primary structure and surface exposure of the major outer membrane protein (MOMP) isolated from 14C intrinsically or 125I extrinsically radiolabeled Chlamydia trachomatis serotypes D/UW-3, G/UW-57, H/UW-4, I/UW-12, and L2/434 and the Chlamydia psittaci meningopneumonitis strain were analyzed by two different peptide-mapping techniques. Radiolabeled proteins were digested with either Staphylococcus aureus V8 protease, the patterns of peptide fragments produced being displayed by sodium dodecyl sulfate gel electrophoresis, or alpha-chymotrypsin, the peptides being analyzed after separation by high-voltage electrophoresis and thin-layer chromatography. The comparative structural data obtained from these two different techniques were remarkably similar. From these data, the following points could be made. (i) MOMPs are structurally heterogeneous between members of chlamydial species; the C. psittaci MOMP was clearly distinct from each of the C. trachomatis MOMPs. (ii) Considerable structural homology occurs among MOMPs from different C. trachomatis serotypes; however, distinct differences in the primary structure of each C. trachomatis MOMP were evident. (iii) These observed differences were most obvious in peptide maps of MOMPs isolated from chlamydiae that had been surface labeled by lactoperoxidase-mediated radioiodination. The surface-exposed portions of the MOMPs from serotypes L2 and D were very similar. In contrast, those from serotypes G, H, and I were quite different. These structural data are in agreement with the serospecificities described for these proteins.