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J. Biol. Chem., Vol. 282, Issue 44, 31844-31851, November 2, 2007

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Molecular Identification of Mammalian Phosphopentomutase and Glucose-1,6-bisphosphate Synthase, Two Members of the -D-Phosphohexomutase Family^*

From the de Duve Institute, Université Catholique de Louvain, B-1200 Brussels, Belgium

The molecular identity of mammalian phosphopentomutase has not yet been established unequivocally. That of glucose-1,6-bisphosphate synthase, the enzyme that synthesizes a cofactor for phosphomutases and putative regulator of glycolysis, is completely unknown. In the present work, we have purified phosphopentomutase from human erythrocytes and found it to copurify with a 68-kDa polypeptide that was identified by mass spectrometry as phosphoglucomutase 2 (PGM2), a protein of the -D-phosphohexomutase family and sharing about 20% identity with mammalian phosphoglucomutase 1. Data base searches indicated that vertebrate genomes contained, in addition to PGM2, a homologue (PGM2L1, for PGM2-like 1) sharing about 60% sequence identity with this protein. Both PGM2 and PGM2L1 were overexpressed in Escherichia coli, purified, and their properties were studied. Using catalytic efficiency as a criterion, PGM2 acted more than 10-fold better as a phosphopentomutase (both on deoxyribose 1-phosphate and on ribose 1-phosphate) than as a phosphoglucomutase. PGM2L1 showed only low (<5%) phosphopentomutase and phosphoglucomutase activities compared with PGM2, but was about 5–20-fold better than the latter enzyme in catalyzing the 1,3-bisphosphoglycerate-dependent synthesis of glucose 1,6-bisphosphate and other aldose-bisphosphates. Furthermore, quantitative real-time PCR analysis indicated that PGM2L1 was mainly expressed in brain where glucose-1,6-bisphosphate synthase activity was previously shown to be particularly high. We conclude that mammalian phosphopentomutase and glucose-1,6-bisphosphate synthase correspond to two closely related proteins, PGM2 and PGM2L1, encoded by two genes that separated early in vertebrate evolution.

Received for publication, August 16, 2007 , and in revised form, September 3, 2007.

^* This work was supported in part by grants from the Juvenile Diabetes Foundation International, the Interuniversity Attraction Poles Program-Belgian Science Policy (Network P6/5), and the Concerted Research Action Program of the French Community of Belgium. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Fellow of the Fonds pour l'Encouragement à la Recherche dans l'Industrie et dans l'Agriculture.

² Collaborateur logistique F.R.S.-FNRS.

³ Chercheur qualifié of the Fonds National de la Recherche Scientifique.

⁴ To whom correspondence should be addressed: UCL 7539, Ave. Hippocrate 75, B-1200 Brussels, Belgium. Tel.: 3227647564; Fax: 327647598; E-mail: emile.vanschaftingen{at}uclouvain.be.

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