Allouch Julie, Helbert William, Henrissat Bernard, Czjzek Mirjam
Architecture et Fonction de la Macromolécules Biologiques, UMR 6098, Centre National de la Recherche Scientifique and Universités Aix-Marseille I and II, 31 chemin Joseph Aiguier, F-13402 Marseille Cedex 20, France [corrected]
Structure. 2004 Apr;12(4):623-32. doi: 10.1016/j.str.2004.02.020.
Agarose is a gel-forming polysaccharide with an alpha-L(1,4)-3,6-anhydro-galactose, beta-D(1,3)-galactose repeat unit, from the cell walls of marine red algae. beta-agarase A, from the Gram-negative bacterium Zobellia galactanivorans, is secreted to the external medium and degrades agarose with an endo-mechanism. The structure of the inactive mutant beta-agarase A-E147S in complex with agaro-octaose has been solved at 1.7 A resolution. Two oligosaccharide chains are bound to the protein. The first one resides in the active site channel, spanning subsites -4 to -1. A second oligosaccharide binding site, on the opposite side of the protein, was filled with eight sugar units, parallel to the active site. The crystal structure of the beta-agarase A with agaro-octaose provides detailed information on agarose recognition in the catalytic site. The presence of the second, parallel, binding site suggests that the enzyme might be able to unwind the double-helical structure of agarose prior to the catalytic cleavage.
琼脂糖是一种凝胶形成多糖，其具有α-L(1,4)-3,6-脱水半乳糖、β-D(1,3)-半乳糖重复单元，来源于海洋红藻的细胞壁。来自革兰氏阴性菌食半乳糖栖热袍菌的β-琼脂酶A被分泌到外部培养基中，并以内切机制降解琼脂糖。无活性突变体β-琼脂酶A-E147S与琼脂八糖复合物的结构已在1.7埃分辨率下解析。两条寡糖链与该蛋白质结合。第一条位于活性位点通道中，跨越亚位点-4至-1。在蛋白质的另一侧，第二个寡糖结合位点填充有八个糖单元，与活性位点平行。β-琼脂酶A与琼脂八糖的晶体结构提供了关于催化位点中琼脂糖识别的详细信息。第二个平行结合位点的存在表明该酶可能能够在催化切割之前解开琼脂糖的双螺旋结构。
