Effects of cysteine mutagenesis and loop and strand deletions on surface exposure of MOMP. A. Replacement of all 9 cysteine residues in C. trachomatis MOMP by alanine residues fails to prevent surface exposure. BL: non-expressing BL21 cells; mature: cells expressing mature MOMP without a leader sequence; oT-leader and n-leader, cells expressing MOMPs with ompT and native leaders, respectively. B. Removal of loops containing putative external VS domains (shown in Fig. 6A) fails to prevent surface exposure. TR: cells expressing mature MOMP; nL-TR: unmodified MOMP with its native leader. C. Removal of putative β-strand regions illustrated in Fig. 6B–C prevents surface exposure. Each result is representative of at least 3 similar experiments.