Type II Fatty Acid Synthesis Is Essential for the Replication of Chlamydia trachomatis *

The major phospholipid classes of the obligate intracellular bacterial parasite Chlamydia trachomatis are the same as its eukaryotic host except that they also contain chlamydia-made branched-chain fatty acids in the 2-position. Genomic analysis predicts that C. trachomatis is capable of type II fatty acid synthesis (FASII). AFN-1252 was deployed as a chemical tool to specifically inhibit the enoyl-acyl carrier protein reductase (FabI) of C. trachomatis to determine whether chlamydial FASII is essential for replication within the host. The C. trachomatis FabI ( Ct FabI) is a homotetramer and exhibited typical FabI kinetics, and its expression complemented an Escherichia coli fabI (Ts) strain. AFN-1252 inhibited Ct FabI by binding to the FabI·NADH complex with an IC 50 of 0.9 μ m at saturating substrate concentration. The x-ray crystal structure of the Ct FabI·NADH·AFN-1252 ternary complex revealed the specific interactions between the drug, protein, and cofactor within the substrate binding site. AFN-1252 treatment of C. trachomatis -infected HeLa cells at any point in the infectious cycle caused a decrease in infectious titers that correlated with a decrease in branched-chain fatty acid biosynthesis. AFN-1252 treatment at the time of infection prevented the first cell division of C. trachomatis, although the cell morphology suggested differentiation into a metabolically active reticulate body. These results demonstrate that FASII activity is essential for C. trachomatis proliferation within its eukaryotic host and validate Ct FabI as a therapeutic target against C. trachomatis.