Abstract
UDP-arabinopyranose mutase (UAM), which catalyzes to interconvert UDP-arabinopyranose and UDP-arabinofuranose, is essential for production of arabinofuranose-containing polysaccharides and glycoproteins. UAM is identical to plant polypeptides previously known as reversibly glycosylated polypeptides (RGPs) which reversibly bind UDP-Glc to give glucosylated polypeptides. Little is known about the catalytic mechanism and there is controversy that RGPs have other functions besides mutase. We now report identification of glycosylated residues.
LC/MS analysis revealed that glucosyl residue from UDP-Glc linked to Arg158. We generated the recombinant proteins from which some arginines were substituted for alanine. Mutase activity was not detected in an R158A mutant protein. The mutase activity of an R151A mutant was the same as wild type, but of R165A decreased to 6% of wild one. From the results, it was concluded that Arg158 of UAM was the sugar-binding amino acid residue, and the RGP and mutase activities occurred on same Arg158.
