nucleotide 5 u2032 triphosphate atp adenosine 5 u2032 triphosphate ctp cytidine 5 u2032 triphosphate gtp guanosine 5 u2032 triphosphate utp uridine 5 u2032 triphosphate datp 2 u2032 deoxyadenosine 5 u2032 triphosphate dctp 2 u2032 deoxycytidine 5 u2032 triphosphate dgtp 2 u2032 deoxyguanosine 5 u2032 triphosphate dttp 2 u2032 deoxythymidine 5 u2032 triphosphate ndp sugar nucleotide diphosphosugar iptg isopropyl u03b2 d thiogalactopyranoside and wt wild type glycosyltransferases gts an essential class of ubiquitous enzymes are generally perceived as unidirectional catalysts however the present invention teaches that gts catalyze readily reversible reactions allowing sugars and aglycons to be exchanged thus the reversibility of gt catalyzed reactions is useful for the rapid synthesis of exotic nucleotide sugars establishing in vitro gt activity in complex systems and enhancing natural product diversity the present invention is based on the inventors 39 success in broadening the promiscuity of a natural product gt u2014 the oleandomycin gt oled from streptomyces antibioticus the native macrolide gt reaction catalyzed by oled was previously characterized and is shown in fig4 using a high throughput screen based upon a fluorescent glycoside donor the inventors have identified from a small library of random oled mutants a number of oled variants with improved activities toward a range of alternative donor substrates this work provides a template for engineering other natural product gts and highlights variant gts for the glycorandomization of a range of therapeutically important acceptors including aminocoumarins flavonoids and macrolides another aspect of the invention is a versatile method for optimizing glycosyltransferases such as oled toward.