Identification by sequence analysis of two-site posttranslational processing of the cysteine-rich outer membrane protein 2 of Chlamydia trachomatis serovar L2

The 60,000-molecular-weight cysteine-rich outer membrane protein (OMP2) from Chlamydia trachomatis participates in the disulfide-mediated outer-membrane organization unique to this organism. In addition, this protein is a primary focus of the host immune response. We cloned and sequenced the gene for OMP2 from C. trachomatis serovar L2. A lambda gt11 recombinant that expressed an antigenic portion of this protein was selected by antibody screening and provided a probe for the selection in lambda 1059 of a clone containing the entire gene. DNA sequencing of this clone identified one open reading frame of 1,641 base pairs, starting with a methionine codon and coding for a polypeptide with a molecular weight of 58,792. Amino-terminal protein sequencing and analysis of the translated DNA sequence demonstrated that processing at alternate signal peptide cleavage sites accounts for the molecular-weight polymorphism of this protein. The mature proteins had a net positive charge and contained 24 cysteine residues.