HETEROLOGOUSLY EXPRESSED ACYL CARRIER PROTEIN DOMAIN OF RAT FATTY-ACID SYNTHASE FUNCTIONS IN ESCHERICHIA-COLI FATTY-ACID SYNTHASE AND STREPTOMYCES-COELICOLOR POLYKETIDE SYNTHASE SYSTEMS

Introduction: Fatty acid synthases (FASs) catalyze the de novo biosynt hesis of long-chain saturated fatty acids by a process common to eubac teria and eukaryotes, using either a set of monofunctional proteins (T ype II FAS) or a polypeptide containing several catalytic functions (T ype I FAS). To compare the features of a Type I domain with its Type I I counterpart we expressed and characterized an acyl carrier protein ( ACP) domain of the Type I rat FAS. Results: An ACP domain of rat FAS w as defined that allows expression of a small percentage of active holo -ACP both in Escherichia coil, increasing fivefold upon co-expression with an E. coil holo-ACP synthase, and in Streptomyces coelicolor. The rat ACP domain functions with some components of the E. coil FAS, and can replace the actinorhodin polyketide synthase (PKS) ACP in S. coel icolorA3(2), Purification of the rat ACP domain from E. coil resulted in loss of its functionality. Purified apo-ACP could be converted to i ts holo-form upon incubation with purified E. coli holo-ACP synthase i n vitro, however, suggesting that the loss of functionality was not du e to a conformational change, Conclusions: Functionality of the recomb inant rat ACP was shown in distantly related and diverse enzyme system s, suggesting that Type I and Type II ACPs have a similar conformation . A procedure was described that might permit the production of rat FA S holo-ACP for structural and further biochemical characterization.