Starch phosphorylase: Role in starch metabolism and biotechnological applications

Abstract

The alpha-glucan phosphorylases of the glycosyltransferase family are important enzymes of carbohydrate metabolism in prokaryotes and eukaryotes. The plant alpha-glucan phosphorylase, commonly called starch phosphorylase (EC 2.4.1.1), is largely known for the phosphorolytic degradation of starch. Starch phosphorylase catalyzes the reversible transfer of glucosyl units from glucose-1-phosphate to the nonreducing end of alpha-1,4-D-glucan chains with the release of phosphate. Two distinct forms of starch phosphorylase, plastidic phosphorylase and cytosolic phosphorylase, have been consistently observed in higher plants. Starch phosphorylase is industrially useful and a preferred enzyme among all glucan phosphorylases for phosphorolytic reactions for the production of glucose-1-phosphate and for the development of engineered varieties of glucans and starch. Despite several investigations, the precise functional mechanisms of its characteristic multiple forms and the structural details are still eluding us. Recent discoveries have shed some light on their physiological substrates, precise biological functions, and regulatory aspects. In this review, we have highlighted important developments in understanding the role of starch phosphorylases and their emerging applications in industry.

Enzyme-catalyzed chemical structure-controlling template polymerization

“…42 Again, altered reaction conditions allow to shift the reaction equilibrium towards the polymer (amylose), and the bond formation between the monomers occurs at the active site of the enzyme and the enzyme's substrate binding sites control the sequence of the reaction product obtained. …”

Starch-related enzymes during potato tuber dormancy and sprouting

“…Starch degrada tion coincides with enhanced activities of α amy lase, β amylase, starch phosphorylase (STP), mal tase, and debranching enzymes, as well as the accu mulation of their products. Among all these enzymes, STP catalyzes a reversible reaction: the conversion from starch n to starch n-1 and glucose 1 phosphate (using inorganic phosphate) and vice versa, implying that this enzyme could be involved in both starch syn thesis and breakdown [6].…”

Role of Glycoside Phosphorylases in Mannose Foraging by Human Gut Bacteria

“…In GH reaction mechanisms, the nucleophilic attack of the C-1 of the glycoside is performed by a water molecule activated by the catalytic base. The natural structural and functional diversity of GPs thus appears to be highly restricted because of the following: (i) they are found in only 7 of the 226 GH and GT families listed in the CAZy database (March 2013); (ii) approximately only 15 EC entries are currently assigned to GPs (24); (iii) their specificity toward glycosyl phosphates is limited to ␣-and ␤-D-glucopyranose 1-phosphate (25)(26)(27)(28)(29), which are the most prevalent substrates; ␣-D-galactopyranose 1-phosphate (30); N-acetyl-␣-D-glucosamine 1-phosphate (31), and ␣-Dmannopyranose 1-phosphate (32). In July 2013, ␣-D-mannopyranose 1-phosphate specificity was described for just one enzyme produced by a human gut bacterium, the Bacteroides fragilis NCTC 9343 mannosylglucose phosphorylase (BfMP), FIGURE 1.…”