1rmg

From Proteopedia

---

Revision as of 23:35, 20 November 2007

proteopedia linkproteopedia link

spinqualitylabelsall models 1rmg, resolution 2.0Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

RHAMNOGALACTURONASE A FROM ASPERGILLUS ACULEATUS

Overview

BACKGROUND: Pectic substances are the major polysaccharide components of, the middle lamella and primary cell wall of dicotyledonous plants. They, consist of homogalacturonan 'smooth' regions and highly rhamnified 'hairy', regions of rhamnogalacturonan. The backbone in rhamnogalacturonan-l, (RG-l), which is composed of alternating galacturonic acid and rhamnose, residues, is the substrate for a new class of enzymes known as, rhamnogalacturnoases (RGases). RGase A is a novel enzyme implicated in the, enzymatic degradation of RG-l. RESULTS: The structure of RGase A from, Aspergillus aculeatus has been solved by the single isomorphous, replacement method including anomalous scattering (SIRAS method) to 2.0 A, resolution. The enzyme folds into a large right-handed parallel beta, helix, with a core composed of 13 turns of beta strands. Four parallel, beta sheets (PB1, PB1a, PB2 and PB3), formed by the consecutive turns, are, typically separated by a residue in the conformation of a left-handed, alpha helix. As a consequence of the consecutive turns, 32% of all, residues have their sidechains aligned at the surface or in the interior, of the parallel beta helix. The aligned residues at the surface are, dominated by threonine, aspartic acid and asparagine, whereas valine, leucine and isoleucine are most frequently found in the interior. A very, large hydrophobic cavity is found in the interior of the parallel beta, helix. The potential active site is a groove, oriented almost, perpendicular to the helical axis, containing a cluster of three aspartic, acid residues and one glutamic acid residue. The enzyme is highly, glycosylated; two N-linked and eighteen O-linked glycosylation sites have, been found in the structure. CONCLUSIONS: Rhamnogalacturonase A from A., aculeatus is the first three-dimensional structure of an enzyme, hydrolyzing glycoside bonds within the backbone of RG-l. The large groove, which is the potential active site of RGase A, is also seen in the, structures of pectate lyases. Two catalytic aspartic acid residues, which, have been proposed to have a catalytic role, reside in this area of RGase, A. The distance between the aspartic acid residues is consistent with the, inverting mechanism of catalysis. The glycan groups bound to RGase A are, important to the stability of the crystal, as the carbohydrate moiety is, involved in most of the intermolecular hydrogen bonds.

About this Structure

1RMG is a Single protein structure of sequence from Aspergillus aculeatus with MAN, BMA and GLC as ligands. Full crystallographic information is available from OCA.

Reference

The crystal structure of rhamnogalacturonase A from Aspergillus aculeatus: a right-handed parallel beta helix., Petersen TN, Kauppinen S, Larsen S, Structure. 1997 Apr 15;5(4):533-44. PMID:9115442

Page seeded by OCA on Wed Nov 21 01:42:37 2007