Perrakis A, Tews I, Dauter Z, Oppenheim A B, Chet I, Wilson K S, Vorgias C E
European Molecular Biology Laboratory, Hamburg, Germany.
Structure. 1994 Dec 15;2(12):1169-80. doi: 10.1016/s0969-2126(94)00119-7.
Chitinases cleave the beta-1-4-glycosidic bond between the N-acetyl-D-glucosamine units of which chitin is comprised. Chitinases are present in plants, bacteria and fungi, but whereas structures are available for two prototypic plant enzymes, no structure is available for a bacterial or fungal chitinase.
To redress this imbalance, the structure of native chitinase A from Serratia marcescens has been solved by multiple isomorphous replacement and refined at 2.3 A resolution, resulting in a crystallographic R-factor of 16.2%. The enzyme comprises three domains: an all beta-strand amino-terminal domain, a catalytic alpha/beta-barrel domain, and a small alpha+beta-fold domain. There are several residues with unusual geometries in the structure. Structure determination of chitinase A in complex with N,N',N",N"'-tetra-acetylo-chitotetraose, together with biochemical and sequence analysis data, enabled the positions of the active-site and catalytic residues to be proposed.
The reaction mechanism seems to be similar to that of lysozyme and most other glycosylhydrolases, i.e. general acid-base catalysis. The role of the amino-terminal domain could not be identified, but it has similarities to the fibronectin III domain. This domain may possibly facilitate the interaction of chitinase A with chitin.
几丁质酶可切割构成几丁质的N - 乙酰 - D - 葡糖胺单元之间的β-1,4 - 糖苷键。几丁质酶存在于植物、细菌和真菌中，但尽管已有两种典型植物酶的结构，却尚无细菌或真菌几丁质酶的结构。
为纠正这种不平衡，通过多重同晶置换法解析了粘质沙雷氏菌天然几丁质酶A的结构，并在2.3埃分辨率下进行了精修，得到的晶体学R因子为16.2%。该酶由三个结构域组成：一个全β链氨基末端结构域、一个催化性α/β桶状结构域和一个小的α + β折叠结构域。结构中存在几个具有异常几何形状的残基。几丁质酶A与N,N',N",N"'-四乙酰壳四糖复合物的结构测定，结合生化和序列分析数据，使得能够提出活性位点和催化残基的位置。
反应机制似乎与溶菌酶和大多数其他糖基水解酶相似，即一般酸碱催化。氨基末端结构域的作用尚无法确定，但它与纤连蛋白III结构域有相似之处。该结构域可能有助于几丁质酶A与几丁质的相互作用。
