Hazlewood G P, Davidson K, Laurie J I, Huskisson N S, Gilbert H J
Department of Biochemistry, AFRC Institute of Animal Physiology and Genetics Research, Babraham, Cambridge, UK.
J Gen Microbiol. 1993 Feb;139(2):307-16. doi: 10.1099/00221287-139-2-307.
The Clostridium thermocellum celI gene, coding for endoglucanase I (CelI), consists of an open reading frame (ORF) of 2640 nucleotides and codes for a protein of M(r) 98531. The ORF was confirmed as celI by comparing the N-terminal sequence of purified recombinant CelI with that deduced from the nucleotide sequence. CelI hydrolysed lichenan and carboxymethylcellulose, but was principally active against barley beta-glucan. It exhibited significant sequence identity with subfamily E2 endoglucanases, and by analogy with others in this group contains a catalytic domain of around 500 residues located in the N-terminal half of the protein. The C-terminal region of CelI was highly homologous with the cellulose-binding domain of the non-catalytic cellulosome subunit, S1. A repeated segment, previously shown to be highly conserved in xylanase Z and in other endoglucanases from C. thermocellum, was absent from CelI. Antiserum raised against purified recombinant CelI cross-reacted with proteins contained in the cellulosomes of two strains of C. thermocellu, suggesting that CelI is either a component of the cellulosome or is homologous to other cellulosome proteins. A second gene, located upstream of celI, consisted of an ORF of 1671 nucleotides, coding for a protein of M(r) 61042. Based on its homology with the Escherichia coli tar gene product, the polypeptide encoded by the second gene is tentatively identified as a sensory transducer.
嗜热栖热梭菌的celI基因编码内切葡聚糖酶I（CelI），由一个2640个核苷酸的开放阅读框（ORF）组成，编码的蛋白质分子量为98531。通过比较纯化的重组CelI的N端序列与从核苷酸序列推导的序列，证实该ORF为celI。CelI能水解地衣多糖和羧甲基纤维素，但主要对大麦β-葡聚糖有活性。它与E2亚家族内切葡聚糖酶具有显著的序列同一性，并且与该组中的其他酶类似，在蛋白质的N端一半含有一个约500个残基的催化结构域。CelI的C端区域与非催化性纤维小体亚基S1的纤维素结合结构域高度同源。CelI中不存在一个先前在木聚糖酶Z和嗜热栖热梭菌的其他内切葡聚糖酶中高度保守的重复片段。针对纯化的重组CelI产生的抗血清与两株嗜热栖热梭菌的纤维小体中的蛋白质发生交叉反应，这表明CelI要么是纤维小体的一个组成部分，要么与其他纤维小体蛋白同源。位于celI上游的第二个基因由一个1671个核苷酸的ORF组成，编码一个分子量为61042的蛋白质。基于其与大肠杆菌tar基因产物的同源性，第二个基因编码的多肽被初步鉴定为一种传感转导器。
