The biosynthesis of the enediyne moiety of the antitumor natural product calicheamicin
involves an iterative polyketide synthase (CalE8) and other ancillary enzymes. In the
proposed mechanism for the early stage of 10-membered enediyne biosynthesis, CalE8
produces a carbonyl-conjugated polyene with the assistance of a putative thioesterase
(CalE7). We have determined the x-ray crystal structure of CalE7 and found that the subunit
adopts a hotdog fold with an elongated and kinked substrate-binding channel embedded …