ARCHITECTURE OF THE CELL-ENVELOPE OF CHLAMYDIA-PSITTACI 6BC

The cysteine-rich envelope proteins of the elementary body form of chl amydiae are thought to be located in the outer membrane on the basis o f their insolubility in the weak anionic detergent N-lauryl sarcosinat e (Sarkosyl). We found, however, that the insolubility of the small (E nvA) and the large (EnvB) cysteine-rich proteins of Chlamydia psittaci 6BC in Sarkosyl is dependent on the maintenance of a supramolecular d isulfide-cross-linked complex and is unlikely to be a valid indicator of outer membrane location. Consequently, we used other methods to cha racterize the architecture of the cell envelope of C. psittaci 6BC. We found that disulfide-reduced EnvA, previously sho,m to be a lipoprote in, segregated into the detergent phase during Triton X-114 partitioni ng experiments and was recovered from the membrane fraction of element ary bodies lysed by nondetergent means. In contrast, disulfide-reduced EnvB segregated to the aqueous phase in partitioning experiments and was found in the soluble fraction of elementary bodies lysed in the ab sence of detergents. The hydrophobic affinity probe 3-(trifluoromethyl )-3-(m-[I-125] iodophenyl)-diazirine labeled the major outer membrane protein and EnvA but did not label EnvB. Treatment of intact elementar y bodies of C. psittaci with trypsin had no effect on the cysteine-ric h proteins; although the major outer membrane protein was partially de graded. On the basis of these and other observations, we propose that EnvA is anchored to the outer membrane by its lipid moiety, with a hyd rophilic peptide portion extending into the periplasm, and that EnvB i s located exclusively within the periplasm. We further propose that di sulfide cross-linked polymers of EnvB are the functional equivalent of peptidoglycan, forming a disulfide cross-linked network with the peri plasmic domains of EnvA and other membrane proteins, which accounts fo r the osmotic stability of elementary bodies.