Chitlaru E, Roseman S
Department of Biology and the McCollum-Pratt Institute, The Johns Hopkins University, Baltimore, Maryland 21218, USA.
J Biol Chem. 1996 Dec 27;271(52):33433-9. doi: 10.1074/jbc.271.52.33433.
The accompanying papers (Keyhani, N. O., and Roseman, S. (1996) J. Biol. Chem. 271, 33414-33424; Keyhani, N. O., and Roseman, S. (1996) J. Biol. Chem. 271, 33425-33432) describe two unique beta-N-acetylglucosaminidases from Vibrio furnissii. A third, ExoII, is reported here. The gene, exoII, was cloned into Escherichia coli, sequenced, and ExoII purified to apparent homogeneity (36 kDa). The molecular weight and N-terminal 16 amino acids of the protein conform to the predicted sequence. ExoII exhibited unique substrate specificity. It rapidly cleaved p-nitrophenyl and 4-methylumbelliferyl beta-GlcNAc, was slightly active with p-nitrophenyl-beta-GalNAc, and was inactive with all other GlcNAc derivatives tested, including N,N'-diacetylchitobiose and (GlcNAc)n, n = 3-6. Unlike GlcNAc (Ki, 210 microM), (GlcNAc)n are poor inhibitors of ExoII. The predicted protein sequence is unique among beta-N-acetylglucosaminidases excepting Cht60, recently cloned from a marine Alteromonas (Tsujibo, H., Fujimoto, K., Tanno, H., Miyamoto, K., Imada, C., Okami, Y., and Inamori, Y. (1994) Gene (Amst.) 146, 111-115). Cht60, a chitobiase, is 26.9% identical to ExoII in a 182-amino acid overlap, but the two enzymes differ in substrate specificity and other properties. ExoII shares similarity with five bacterial and yeast beta-glucosidases, up to 44% identity in the 25-amino acid catalytic domain. By analogy, ExoII may play a role in signal transduction between invertebrate hosts and V. furnissii.
随附论文（凯哈尼，N. O.，和罗斯曼，S.（1996年）《生物化学杂志》271卷，33414 - 33424页；凯哈尼，N. O.，和罗斯曼，S.（1996年）《生物化学杂志》271卷，33425 - 33432页）描述了来自弗氏弧菌的两种独特的β - N - 乙酰氨基葡萄糖苷酶。本文报道了第三种，即外切酶II。外切酶II基因（exoII）被克隆到大肠杆菌中，进行了测序，并将外切酶II纯化至表观均一性（36 kDa）。该蛋白质的分子量和N端16个氨基酸与预测序列相符。外切酶II表现出独特的底物特异性。它能快速切割对硝基苯基和4 - 甲基伞形酮基β - GlcNAc，对硝基苯基 - β - GalNAc略有活性，而对所有其他测试的GlcNAc衍生物均无活性，包括N，N' - 二乙酰壳二糖和（GlcNAc）n（n = 3 - 6）。与GlcNAc（Ki，210 μM）不同，（GlcNAc）n是外切酶II的弱抑制剂。除了最近从海洋交替单胞菌中克隆的Cht60（辻场，H.，藤本，K.，田野，H.，宫本，K.，今田，C.，冈见，Y.，和稻森，Y.（1994年）《基因》（阿姆斯特丹）146卷，111 - 115页）外，预测的蛋白质序列在β - N - 乙酰氨基葡萄糖苷酶中是独特的。Cht60是一种壳二糖酶，在182个氨基酸的重叠区域与外切酶II有26.9%的同一性，但这两种酶在底物特异性和其他特性上有所不同。外切酶II与五种细菌和酵母β - 葡萄糖苷酶有相似性，在25个氨基酸的催化结构域中同一性高达44%。由此类推，外切酶II可能在无脊椎动物宿主与弗氏弧菌之间的信号转导中发挥作用。
