Beintema J J, Terwisscha van Scheltinga A C
Department of Biochemistry, Rijksuniversiteit Groningen, Nijenborgh, The Netherlands.
EXS. 1996;75:75-86. doi: 10.1007/978-3-0348-9225-4_5.
Structural and functional features of plant lysozymes are reviewed. All lysozymes also have chitinase activity, but not all plant chitinases are also lysozymes. However, for many chitinases it is not yet known if they also possess lysozyme activity. Enzymes with lysozyme activity occur in different, structurally unrelated, families of chitinases. Plant chitinases with lysozyme activity are basic enzymes with high isoionic points. Their lysozyme activities have a shart pH optimum around pH 4.5-5.0, while they show chitinase activities in a much broader pH range. High lysozyme activities are observed at low ionic strength values (0.05). The X-ray structure of a lysozyme/chitinase from latex of the rubber tree, Hevea brasiliensis, is presented. This enzyme is also known under the name hevamine. It belongs to the family 18 or h-type chitinases (also called class III chitinases). The structure consists of an alpha/beta barrel fold, which has not been found in other chitinase or lysozyme structures. A glutamic acid residue may be catalytically active in the substrate-binding cleft of the enzyme. Other plant lysozymes are homologous with the family 19 or b-type chitinases (class I, II and IV). The X-ray structure of barley chitinase, a representative of this family with negligible lysozyme activity, has a similar folding as found in animal and phage lysozymes.
本文综述了植物溶菌酶的结构和功能特征。所有溶菌酶也都具有几丁质酶活性，但并非所有植物几丁质酶都是溶菌酶。然而，对于许多几丁质酶而言，它们是否也具有溶菌酶活性尚不清楚。具有溶菌酶活性的酶存在于不同的、结构上不相关的几丁质酶家族中。具有溶菌酶活性的植物几丁质酶是具有高等电点的碱性酶。它们的溶菌酶活性在pH值约4.5 - 5.0时具有较窄的最佳pH范围，而它们在更宽的pH范围内显示出几丁质酶活性。在低离子强度值（0.05）下观察到高溶菌酶活性。本文还展示了来自橡胶树（巴西橡胶树）乳胶的一种溶菌酶/几丁质酶的X射线结构。这种酶也被称为橡胶树溶菌酶。它属于第18家族或h型几丁质酶（也称为III类几丁质酶）。其结构由α/β桶状折叠组成，这在其他几丁质酶或溶菌酶结构中尚未发现。一个谷氨酸残基可能在该酶的底物结合裂隙中具有催化活性。其他植物溶菌酶与第19家族或b型几丁质酶（I、II和IV类）同源。大麦几丁质酶是该家族中溶菌酶活性可忽略不计的一个代表，其X射线结构与动物和噬菌体溶菌酶中的折叠结构相似。
