 In the final step, the product of ColD, GDP-4-keto-3,6-dideoxymannose, reacts with ColC, which reduces the ketone functionality at C-4 back to an alcohol and inverts the configuration about C-5.The resulting product, GDP-L-colitose, is then incorporated into the O-antigen by glycosyltransferases and "O"-antigen processing proteins.Further reactions join the O-antigen to the core polysaccharide to form the full lipopolysaccharide.