Tetrasaccharide substrate, binding

The best available example to understand how the sulfotransferases interact with their substa tes is from the study of the structure of a ternary complex of 3-OST-3/PAP/tetrasaccharide (where PAP represents 3 -phosphoadenosine 5 -phosphate). From this structure, one can clearly observe e interaction between the amino acid residues that participate in the binding to the substrate. The 3-OH position of the glucosamine unit (acceptor site) is locked into a position that is about 2.8 A to the catalytic base residue. At least sbc amino acid residues interact with the different functional groups of the saccharide units around the reducing end and the nonreducing end of the glucosamine acceptor (Figure 10). 

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