Abstract
Glycogen is a highly branched α-glucan polymer widely used as energy and carbon reserve by many microorganisms. The branches are introduced by glycogen branching enzymes (EC 2.4.1.18), that are classified into glycoside hydrolase families 13 (GH13) and 57 (GH57). Most microorganisms have typically only a single glycogen branching enzyme (gbe) gene. Only a few microorganisms carry both GH13 and GH57 gbe genes, such as Petrotoga mobilis and Mycobacterium tuberculosis. Here we report the basic characteristics of the GH13 and GH57 GBE of P. mobilis, both heterologously expressed in E. coli. The GH13 GBE has a considerably higher branching activity towards the linear α-glucan amylose, and produces a highly branched α-glucan with a high molecular weight which is very similar to glycogen. The GH57 GBE, on the contrary, makes a much smaller branched α-glucan. While the GH13 GBE acts as a classical glycogen branching enzyme involved in glycogen synthesis, the role of GH57 GBE remains unclear.
Highlights
The phylum Thermotogae is currently composed of 50 species spread across 13 genera
DHBS was obtained by debranching highly branched starch (HBS, 8% α-1,6-linkages) with isoamylase and pullulanase; HBS was obtained by modifying gelatinized potato starch with the Branchzyme, an enzyme preparation produced by Novozymes (Bagsvaerd, Denmark) containing the glycogen branching enzyme from Rhodothermus obamensis
The results reported in this paper show that the glycoside hydrolase families 13 (GH13) and the GH57 Glycogen branching enzyme (GBE) of P. mobilis differ considerably with respect to activity towards amylose and the structure of the branched α-glucan produced
Summary
The phylum Thermotogae is currently composed of 50 species spread across 13 genera. All its members have a characteristic outer membrane that lies loosely around the cells. The genera are grouped into 5 families [1, 2]: (i) Fervidobacteriaceae, comprising the genera Fervidobacterium [1] and Thermosipho [3]; (ii) Kosmotogaceae, comprising the genera Kosmotoga [4] and Oceanotoga; (iii) Mesoaciditogaceae, comprising the genera Mesoaciditoga [5, 6] and Athalassotoga; (vi) Petrotogaceae, comprising the genera Petrotoga [7], Defluviitoga [8], Geotoga [7], Marinitoga [9] and Oceanotoga [10]; and (v) Thermotogaceae, comprising the genera Thermotoga and Pseudothermotoga [2]. All the genomes contain the key enzymes for glycogen synthesis, namely ADP-
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