Last Step in the Conversion of Trehalose to Glycogen

Abstract

We show that Mycobacterium smegmatis has an enzyme catalyzing transfer of maltose from [ 14 C]maltose 1-phosphate to glycogen. This enzyme was purified 90-fold from crude extracts and characterized. Maltose transfer required addition of an acceptor. Liver, oyster, or mycobacterial glycogens were the best acceptors, whereas amylopectin had good activity, but amylose was a poor acceptor. Maltosaccharides inhibited the transfer of maltose from [14 C]maltose-1-P to glycogen because they were also acceptors of maltose, and they caused production of larger sized radioactive maltosaccharides. When maltotetraose was the acceptor, over 90% of the 14 C-labeled product was maltohexaose, and no radioactivity was in maltopentaose, demonstrating that maltose was transferred intact. Stoichiometry showed that 0.89 mol of inorganic phosphate was produced for each micromole of maltose transferred to glycogen, and 56% of the added maltose-1-P was transferred to glycogen. This enzyme has been named ␣1,4-glucan:maltose-1-P maltosyltransferase (GMPMT). Transfer of maltose to glycogen was inhibited by micromolar amounts of inorganic phosphate or arsenate but was only slightly inhibited by millimolar concentrations of glucose-1-P, glucose-6-P, or inorganic pyrophosphate. GMPMT was compared with glycogen phosphorylase (GP). GMPMT catalyzed transfer of [ 14 C]maltose-1-P, but not [ 14 C]glucose-1-P, to glycogen, whereas GP transferred radioactivity from glucose-1-P but not maltose-1-P. GMPMT and GP were both inhibited by 1,4-dideoxy-1,4-imino-D-arabinitol, but only GP was inhibited by isofagomine. Because mycobacteria that contain trehalose synthase accumulate large amounts of glycogen when grown in high concentrations of trehalose, we propose that trehalose synthase, maltokinase, and GMPMT represent a new pathway of glycogen synthesis using trehalose as the source of glucose.

α-Glucan biosynthesis and the GlgE pathway in Mycobacterium tuberculosis

“…Interestingly, the existence of M1P in mycobacteria was reported many years ago [49]. So hints of the existence of the GlgE pathway were published before it was discovered [17,18]. Similarly, Fibrobacter succinogenes Ser 85 was reported to produce metabolites consistent with the presence of M1P and maltooligosaccharides [50,51] well before the discovery of the pathway and the identification of the GlgE pathway genes in this organism [2].…”

“…GlgE is a maltosyl transferase (E.C. 2.4.99.16) that uses α-maltose 1-phosphate (M1P) as a donor to generate α-1,4-linkages [17,18]. The M1P disaccharide phosphate is quite distinct from the nucleoside diphospho monosaccharide donor of GlgA glycogen synthase.…”

The α-Glucan Phosphorylase MalP of Corynebacterium glutamicum Is Subject to Transcriptional Regulation and Competitive Inhibition by ADP-Glucose

“…The first alternative pathway proceeds via the rv3032-encoded glycosyltransferase in M. tuberculosis and is mainly involved in the formation of methylglucose lipopolysaccharides (80,81). The second alternative pathway for ␣-glucan formation in mycobacteria proceeds via the consecutive action of the maltokinase Pep1 and the maltosyltransferase GlgE (82,83). The presence of alternative sources of ADPglucose is not relevant for the formation of glycogen in C. glutamicum ⌬glgAC cultivated on maltose observed here, since this strain lacks the glgA-encoded glycogen synthase.…”

Antitubercular Drugs Based on Carbohydrate Derivatives

“…GlgE is an α-1,4-glucan-phosphate maltosyltransferase, and a member of the glycoside hydrolase subfamily GH13_3 in the CAZy database, and a genetically validated tuberculosis drug target [202][203][204][205]. Transposon site hybridization analysis has identified genes essential for optimum growth in MTB [206][207].…”