ETHYL-SUBSTITUTED ERYTHROMYCIN DERIVATIVES PRODUCED BY DIRECTED METABOLIC ENGINEERING

A previously unknown chemical structure, 6-desmethyl-6-ethylerythromyc in A (6-ethylErA), was produced through directed genetic manipulation of the erythromycin (Er)-producing organism Saccharopolyspora erythrae a, In an attempt to replace the methyl side chain at the C-6 position of the Er polyketide backbone with an ethyl moiety, the methylmalonate -specific acyltransferase (AT) domain of the Er polyketide synthase wa s replaced with an ethylmalonate-specific AT domain from the polyketid e synthase involved in the synthesis of the 16-member macrolide niddam ycin, The genetically altered strain was found to produce ErA, however , and not the ethyl-substituted derivative. When the strain was provid ed with precursors of ethylmalonate, a small quantity of a macrolide w ith the mass of 6-ethylErA was produced in addition to ErA, Because su bstrate for the heterologous AT seemed to be limiting, crotonyl-CoA re ductase, a primary metabolic enzyme involved in butyryl-CoA production in streptomycetes, was expressed in the strain. The primary macrolide produced by the reengineered strain was 6-ethylErA.