Diversity-oriented Enzymatic Modular Assembly Of ABO(H)Histo-blood Group Antigens

ABO(H)blood group system is the major human alloantigen system,It is determined by expression of A,B,or H antigens as the terminal carbohydrate epitopes of glycoproteins and glycolipids on the red blood cells.The ABO(H)antigens are not confined to red blood cells but are also widely distributed on epithelial and endothelial cells of all organs,on neurons of the peripheral nervous system and secretion fluids such ashuman milk,saliva and urine.These glycan antigens are responsible for the acute immune response of hemolytic transfusion reaction(HTR),bone marrow and organ transplantation.More and more evidences demonstrated that these glycans play important roles in many bacteria,viruses and parasites infection and tumor metastasis.The structures of ABO(H)antigen determinants comprises three carbohydrate epitopes,including A antigen trisaccharide,B antigen trisaccharide and H antigen disaccharide.Depending on different disaccharide precursors in their biosynthetic pathway,the ABO(H)antigens can be further divided into five subtypes.These disaccharides can be used by 3 differetn glycosyltransferase as substrates for the synthesis ofall 15 naturally occurring antigens.The biological significance and clinical importance of ABO(H)antigens have ensured that their synthesis continues to be of significant interest for decades.In the new millennium,many different approaches have been explored for the synthesis of ABO(H)antigens,such as chemical synthesis,chemoenzymatic synthesis,enzymatic synthesis and whole-cell fermentation.However,traditional chemical synthesis is usually time consuming and labor intensive due to the tedious protecting group manipulation and the extensive purification procedures which are necessary to achieve high purity and structural homogeneity.On the other hand,enzymatic synthesis is limited by the sources and strict substrate specificity of the enzymes used.Besides,due to the difficulty of product isolation,whole-cell fermentation is also not the best choice.Despite numerous synthetic approaches reported so far,the collective synthesis of all 15 naturally occurring ABO(H)antigens has only been achieved through elegant chemical synthesis by Lowary and co-workers recently.Herein we describe a highly efficient enzymatic modular assembly(EMA)strategy for diversity-oriented parallel synthesis of all 15 naturally occurring ABO(H)antigens.The research contains the following three parts:1)Chemical or chemoenzymatic synthesis of 5 different disaccharide precursors.2)Enzymatic modular assembly of all 5 naturally occurring H antigns through one step parallel enzymatic fucosylation.3)Enzymatic modular assembly of all 5 naturally occurring A antigens and 5 naturally occurring B antigens by using two different enzyme modules.The novelties of this study:1)The first enzymatic synthesis of all 15 naturally occurring histo-blood group ABO(H)antigens wasachieved.2)The enzymatic modular assembly(EMA)strategy was developed which provides an operationally simple andelegant access for diversity-oriented parallel synthesis of all 15 ABO(H)antigens in only three steps from 5 readily availabledisaccharide acceptors and 3 monosaccharides as donorprecursors.