Starch phosphorylase: Role in starch metabolism and biotechnological applications

Abstract

The α-glucan phosphorylases of the glycosyltransferase family are important enzymes of carbohydrate metabolism in prokaryotes and eukaryotes. The plant α-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 α-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.

Keywords:

• Plant α-glucan phosphorylase
• plastidic and cytosolic phosphorylase Pho1 (L-SP)
• Pho2 (H-SP)
• starch degradation
• glucan synthesis
• glucose-1-phosphate production

Acknowledgments

The facilities at the School of Biotechnology and Bioinformatics sub-center supported by the Department of Biotechnology, Ministry of Science and Technology, Government of India (DBT) are acknowledged. R.S.R. thanks Science and Engineering Research Council, Department of Science and Technology, Government of India for a Fast-Track scientist award.

Declaration of interest: The authors report no conflicts of interest.