2VNC

Crystal structure of Glycogen Debranching enzyme TreX from Sulfolobus solfataricus

Summary for 2VNC

• Entry DOI: 10.2210/pdb2vnc/pdb
• Related: 2VNB 2VR5 2VUY
• Descriptor: GLYCOGEN OPERON PROTEIN GLGX (2 entities in total)
• Functional Keywords: hydrolase, glycosidase, glycosyl hydrolase
• Biological source: SULFOLOBUS SOLFATARICUS
• Total number of polymer chains: 2
• Total formula weight: 166363.72

Authors

Song, H.-N.,Yoon, S.-M.,Cha, H.,Park, K.-T.,Woo, E.-J. (deposition date: 2008-02-04, release date: 2008-07-29, Last modification date: 2024-11-06)

Primary citation

Woo, E.-J.,Lee, S.,Cha, H.,Park, J.-T.,Yoon, S.-M.,Song, H.-M.,Park, K.-H.
Structural Insight Into the Bifunctional Mechanism of the Glycogen-Debranching Enzyme Trex from the Archaeon Sulfolobus Solfataricus.
J.Biol.Chem., 283:28641-, 2008

PubMed Abstract: TreX is an archaeal glycogen-debranching enzyme that exists in two oligomeric states in solution, as a dimer and tetramer. Unlike its homologs, TreX from Sulfolobus solfataricus shows dual activities for alpha-1,4-transferase and alpha-1,6-glucosidase. To understand this bifunctional mechanism, we determined the crystal structure of TreX in complex with an acarbose ligand. The acarbose intermediate was covalently bound to Asp363, occupying subsites -1 to -3. Although generally similar to the monomeric structure of isoamylase, TreX exhibits two different active-site configurations depending on its oligomeric state. The N terminus of one subunit is located at the active site of the other molecule, resulting in a reshaping of the active site in the tetramer. This is accompanied by a large shift in the "flexible loop" (amino acids 399-416), creating connected holes inside the tetramer. Mutations in the N-terminal region result in a sharp increase in alpha-1,4-transferase activity and a reduced level of alpha-1,6-glucosidase activity. On the basis of geometrical analysis of the active site and mutational study, we suggest that the structural lid (acids 99-97) at the active site generated by the tetramerization is closely associated with the bifunctionality and in particular with the alpha-1,4-transferase activity. These results provide a structural basis for the modulation of activities upon TreX oligomerization that may represent a common mode of action for other glycogen-debranching enzymes in higher organisms.

PubMed: 18703518
DOI: 10.1074/JBC.M802560200

Experimental method

X-RAY DIFFRACTION (3 Å)