Deoxysugar methylation during biosynthesis of the antitumor polyketide elloramycin by Streptomyces olivaceus - Characterization of three methyltransferase genes

The anthracycline-like polyketide drug elloramycin is produced by Streptomy ces olivaceus Tu2353. Elloramycin has antibacterial activity against Gram-p ositive bacteria and also exhibits antitumor activity. From a cosmid clone (cos16F4) containing part of the elloramycin biosynthesis gene cluster, thr ee genes (elmMI, elmMII, and elmMIII) have been cloned. Sequence analysis a nd data base comparison showed that their deduced products resembled S-aden osylmethionine-dependent O-methyltransferases. The genes were individually expressed in Streptomyces albus and also coexpressed with genes involved in the biosynthesis of L-rhamnose, tbe 6-deoxysugar attached to the elloramyc in aglycon, The resulting recombinant strains were used to biotransform thr ee different elloramycin-type compounds: L-rhamnosyl-tetracenomycin C, L-ol ivosyl-tetracenomycin C, and L-oleandrosyl-tetracenomycin, which differ in their 2'-, 3'-, and 4'-substituents of the sugar moieties, When only the th ree methyltransferase-encoding genes elmMI elmMII, and elmMIII were individ ually expressed in S. albus, the methylating activity of the three methyltr ansferases was also assayed in vitro using various externally added glycosy lated substrates, From the combined results of all of these experiments, it is proposed that methyltransferases ElmMI, ElmMII, and ElmMIII are involve d in the biosynthesis of the permethylated L-rhamnose moiety of elloramycin , ElmMI, ElmMII, and ElmMIII are responsible for the consecutive methylatio n of the hydroxy groups at the 2'-, 3'-, and 4'-position, respectively, aft er the sugar moiety has been attached to the aglycon.