Biochemical significance of the non-common amino acid sequences specifying the common functions of enzymes, polysaccharide lyases

多糖裂解酶是催化多糖如藻酸盐、黄原胶、结冷胶和透明质酸盐解聚的酶，所有这些多糖都由细菌产生，并产生寡糖或单糖作为反应产物。该酶严格识别分散在多糖分子上的糖醛酸，并通过β-消除反应在酸性位点裂解多糖。然而，这些酶在它们的一级结构中没有相似性，因此表明这些酶的功能由不同的氨基酸序列编写。为了阐明不同一级结构的酶具有相同底物识别和β-消除反应的原因，测定了鞘氨醇单胞菌A1藻酸盐裂解酶（A1-III）、铜绿假单胞菌PAO 1藻酸盐裂解酶（PA 1167）和芽孢杆菌GL 1黄原胶裂解酶的X-射线晶体结构，并与猪肾N-酰基-D-葡糖胺2-差向异构酶和芽孢杆菌GL 1黄原胶裂解酶的晶体结构进行了比较 关于我们 sp.GL1不饱和葡萄糖醛酸水解酶。这些酶的结构比较表明：（1）A1-III通过使用盖环模块表达β-消除活性。这种结构也在XL中发现，尽管PA 1167没有。(2)A1-III为α/α -barell结构。PA 1167显示反平行β折叠结构。XL为α/α -barrell结构和反胶束β-折叠结构的复合结构。(3)In在所研究的所有多糖裂解酶中，Tyr是必需的催化氨基酸残基，His和Arg参与底物的识别和稳定。从这些结果可以得出结论，即使一级结构不同，通过蛋白质模块的移动，也会产生催化位点和底物识别的相似结构。这一概念表明，蛋白质功能的一级结构的基础上估计并不总是可靠的，并确定蛋白质的功能，应结合它们的三维结构来确定。少

Polysaccharide lyase is an enzyme catalyzing the depolymerization of polysaccharides such as alginate, xanthan, gellan, and hyarunonate, all of which are produced by bacteria, and gives rise oligosaccharides or monosaccharides as reaction products. The enzyme strictly recognizes uronic acids scattered on the polysaccharide molecules and splits the polysaccharides at the acid site through β-elimination reaction. However, these enzymes have no similarities in their primary structures, thus suggesting that the function of these enzymes are written by different amino acid sequences. To elucidate the reason why the enzymes with the different primary structures could show the same substrate recognition and β-elimination reaction, the X-ray crystal structures of Sphingomonas sp. A1 alginate lyase (A1-III), Pseudomonas aeruginosa PAO1 alginate lyase (PA1167), and Bacillus sp.GL1 xanthan lyase were determined and compared with those of porcine kidney N-acyl-D-glucoamine 2-epimerase and Bacillus … More sp.GL1 unsaturated glucuronylhydrolase. The structural comparison of these enzymes indicated that (1)A1-III expresses β-eliination activity by using a lid-loop module. Such the structure is also found in XL, although PA1167 has not. (2) A1-III has α/α -barell structure. PA1167 shows anti-parallel β-sheet structure. XL shows a combined structure of α/α -barrell structure and anti-paralell β-sheet structure. (3)In all the polysaccharide lyases examined, Tyr is an essential catalytic amino acid residue, and His and Arg are involved in the recognition and stabilization of substrate. From these results, it was concluded that, even though the primary structure is different, similar structure for catalytic site and substrate recognition are created through the movement of protein modules. This notion indicates that the estimation of protein function on the basis of primary structure is not always reliable and definitive function of proteins should be determined in combination with the three-dimensional structures of them. Less