Fibrobacter succinogenes 1,3-1,4-β-D-葡聚醣水解酶(Fsβ-glucanase, E.C. 3.2.1.73)主要能特異性水解大麥、小麥與燕麥等穀類植物中的β-D-葡聚糖(β-D-glucan)或地衣聚醣(lichenan)中與β-1,3鍵結相鄰後的β-1,4鍵結,而形成三至五個寡醣組成的最終產物。由截短型Fibrobacter succinogenes 1,3-1,4-β-D-葡聚醣水解酶突變種Y42L晶體結構得知鈣和Tris離子從養晶溶液進入蛋白質共同成為複合物晶體,由酵素動力學實驗得知鈣和Tris離子分別是葡聚醣水解酶的非競爭型與競爭型的抑制劑。突變種結構中有三個鈣離子、二個醋酸根離子及二個Tris離子。除了一個鈣離子與原生種同位置外,另多兩個鈣離子分別位於靠近表面胺基酸Phe152及Glu154和活性區域通道入口處與Asp202有鍵結。其中一個Tris離子的結合位置正好是在催化活性區域-1位置,並與主要催化水解醣苷鍵的胺基酸Glu56及Glu60有氫鍵結合。另一個Tris離子與Phe193及Gly195有氫鍵結合,並與醋酸根離子對同一胺基酸(Phe193)在主鏈和支鏈上互相影響。二個醋酸根離子與鄰近苯環及支鏈之交互作用,可能有助於穩定結構,但不影響催化功能。
Fibrobacter succinogenes 1,3-1,4-β-D-glucanase (Fsβ-glucanase, E.C.3.2.1.73) specifically hydrolyze the β-1,4 bonds when β-1,3 linkages are located prior to the β-1,4 bonds in β-D-glucan or lichenan. The final hydrolyzed products are tri- and penta- saccharides. Three calcium ions and two tris molecules are found in the truncated Fsβ-glucanase mutant Y42L structure. The first calcium ion is located at the same position as that of wild type. The second Ca2+ ion was found near the residues Phe152 and Glu154 on the protein’s surface, and the third one near the active site residue Asp202. Moreover, a tris molecule interacts with the catalytic residues Glu56 and Glu60 at subunit -1 of substrate. Based on the kinetic data, it is shown that the third Ca2+ ion and tris molecule are non-competitive and competitive inhibitors for the enzyme, respectively.
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