Proposed biosynthetic pathway of thailanstatin A (1) in B. thailandensis MSMB43. Crossed domains are inactive or nonfunctional, star-labeled domains are atypical. See text for explanations. A, adenylation; ACP, acyl carrier protein; AT, acyltransferase; C, condensation; DH, dehydratase; ECH, enoyl-CoA hydratase; ER, enoyl reductase; GAT, glyceryl transferase/phosphatase; KR, ketoreductase; KS, ketosynthetase; MT, methyltransferase; OX, FAD-dependent monooxygenase; PCP, peptidyl carrier protein; TE, thioesterase.