Black G W, Rixon J E, Clarke J H, Hazlewood G P, Theodorou M K, Morris P, Gilbert H J
Department of Biological and Nutritional Sciences, University of Newcastle upon Tyne, UK.
Biochem J. 1996 Oct 15;319 ( Pt 2)(Pt 2):515-20. doi: 10.1042/bj3190515.
Xylanase A (XYLA) and arabinofuranosidase C (XYLC) from Pseudomonas fluorescens subsp. cellulosa are modular enzymes consisting of discrete cellulose-binding domains (CBDs) and catalytic domains joined by serine-rich linker sequences. To evaluate the role of the CBDs and interdomain regions, the capacity of full-length and truncated derivatives of the two enzymes, lacking either the linker sequences or CBDs, to hydrolyse a range of substrates, and bind to cellulose, was determined. Removal of the CBDs did not affect either the activity of XYLA or XYLC against soluble arabinoxylan. Similarly, deletion of the linker sequences did not alter the affinity of the enzymes for cellulose or their activity against soluble substrates, even when bound to cellulose via the CBDs. Truncated derivatives of XYLA lacking either the linker sequences or the CBD were less active against xylan contained in cellulose-hemicellulose complexes, compared with the full-length xylanase. Similarly, removal of the CBD from XYLC diminished the activity of the enzyme (XYLC''') against plant-cell-wall material containing highly substituted arabinoxylan. The role of CBDs and linker sequences in the catalytic activity of hemicellulases against the plant cell wall is discussed.
荧光假单胞菌纤维素亚种的木聚糖酶A（XYLA）和阿拉伯呋喃糖苷酶C（XYLC）是模块化酶，由离散的纤维素结合结构域（CBD）和通过富含丝氨酸的连接序列连接的催化结构域组成。为了评估CBD和结构域间区域的作用，测定了这两种酶的全长和截短衍生物（缺失连接序列或CBD）水解一系列底物以及与纤维素结合的能力。去除CBD既不影响XYLA也不影响XYLC对可溶性阿拉伯木聚糖的活性。同样，即使通过CBD与纤维素结合，连接序列的缺失也不会改变酶对纤维素的亲和力或其对可溶性底物的活性。与全长木聚糖酶相比，缺失连接序列或CBD的XYLA截短衍生物对纤维素-半纤维素复合物中所含木聚糖的活性较低。同样，从XYLC中去除CBD会降低该酶（XYLC'''）对含有高度取代阿拉伯木聚糖的植物细胞壁材料的活性。本文讨论了CBD和连接序列在半纤维素酶对植物细胞壁催化活性中的作用。
