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Publication Abstract from PubMed

We present here the first experimental evidence for bound substrate in the active site of a rhamnogalacturonan lyase belonging to family 4 of polysaccharide lyases, Aspergillus aculeatus rhamnogalacturonan lyase (RGL4). RGL4 is involved in the degradation of rhamnogalacturonan-I, an important pectic plant cell wall polysaccharide. Based on the previously determined wild-type structure, enzyme variants RGL4_H210A and RGL4_K150A have been produced and characterized both kinetically and structurally, showing that His210 and Lys150 are key active-site residues. Crystals of the RGL4_K150A variant soaked with a rhamnogalacturonan digest gave a clear picture of substrate bound in the -3/+3 subsites. The crystallographic and kinetic studies on RGL4, and structural and sequence comparison to other enzymes in the same and other PL families, enable us to propose a detailed reaction mechanism for the beta-elimination on [-,2)-alpha-l-rhamno-(1,4)-alpha-d-galacturonic acid-(1,-]. The mechanism differs significantly from the one established for pectate lyases, in which most often calcium ions are engaged in catalysis.

Structural and Biochemical Studies Elucidate the Mechanism of Rhamnogalacturonan Lyase from Aspergillus aculeatus.,Jensen MH, Otten H, Christensen U, Borchert TV, Christensen LL, Larsen S, Leggio LL J Mol Biol. 2010 Sep 17. PMID:20851126^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.