Warren R A, Beck C F, Gilkes N R, Kilburn D G, Langsford M L, Miller R C, O'Neill G P, Scheufens M, Wong W K
Department of Microbiology, University of British Columbia, Vancouver, Canada.
Proteins. 1986 Dec;1(4):335-41. doi: 10.1002/prot.340010407.
Cellulomonas fimi produces an endoglucanase and an exoglucanase which bind strongly to cellulose. Each enzyme contains three distinct regions: a short sequence of about 20 amino acids containing only proline and threonine (the Pro-Thr box); an irregular region, rich in hydroxyamino acids, of low charge density, and which is predicted to have little secondary structure; and an ordered region of higher charge density which contains a potential active site, and which is predicted to have secondary structure. The Pro-Thr box is conserved almost perfectly in the two enzymes. The irregular regions are 50% conserved, and the conserved sequences include four Asn-Xaa-Ser/Thr sites. The ordered regions appear not to be conserved, but the potential active sites both have the sequence Glu-Xaa7-Asn-Xaa6-Thr; they occur at widely separated sites in the two regions. The order of the regions is reversed in the two enzymes: irregular-Pro-Thr box-ordered in the endoglucanase; ordered-Pro-Thr box-irregular in the exoglucanase. The genes for the two enzymes appear to have arisen by shuffling of two conserved sequences and either one or two other sequences.
纤维单胞菌产生一种内切葡聚糖酶和一种外切葡聚糖酶，它们与纤维素紧密结合。每种酶都包含三个不同的区域：一段约20个氨基酸的短序列，仅含脯氨酸和苏氨酸（脯氨酸-苏氨酸盒）；一个不规则区域，富含羟基氨基酸，电荷密度低，预计几乎没有二级结构；以及一个电荷密度较高的有序区域，包含一个潜在的活性位点，预计具有二级结构。脯氨酸-苏氨酸盒在这两种酶中几乎完全保守。不规则区域有50%的保守性，保守序列包括四个天冬酰胺-任一氨基酸-丝氨酸/苏氨酸位点。有序区域似乎不保守，但潜在的活性位点都有谷氨酸-任一氨基酸7-天冬酰胺-任一氨基酸6-苏氨酸序列；它们出现在两个区域中相距很远的位置。这两个区域的顺序在两种酶中是相反的：内切葡聚糖酶中是不规则-脯氨酸-苏氨酸盒-有序；外切葡聚糖酶中是有序-脯氨酸-苏氨酸盒-不规则。这两种酶的基因似乎是由两个保守序列与另外一或两个序列重排产生的。
