Tempelaars C A, Birch P R, Sims P F, Broda P
Department of Biochemistry and Applied Molecular Biology, University of Manchester Institute of Science and Technology, United Kingdom.
Appl Environ Microbiol. 1994 Dec;60(12):4387-93. doi: 10.1128/aem.60.12.4387-4393.1994.
Two cDNA sequences representing putative allelic variants of the Phanerochaete chrysosporium cbhII gene were isolated by hybridization to the Trichoderma reesei cbhII gene. Both of the equivalent genomic sequences were subsequently isolated by the inverse PCR technique. DNA sequencing showed that the cbhII open reading frame of 1,380 bp codes for a putative polypeptide of 460 amino acids which is interrupted by six introns. The domain structure found in T. reesei cbhII is conserved in the equivalent P. chrysosporium protein. The overall similarity between the two gene products is 54%, with the region of highest conservation being found in the cellulose-binding domain (65%). Unlike the cbhI gene of P. chrysosporium, cbhII does not appear to be a member of a class of closely related genes. CBHII is a new member of family B of the beta-1, 4-glucanases. Alignment of the P. chrysosporium and T. reesei CBHII protein sequences showed that all of the residues important for the formation of the extended loops of the catalytic domain and those residues that are involved in the catalytic action of the T. reesei enzyme are also present in the P. chrysosporium equivalent. The profiles of cbh gene expression in P. chrysosporium reveal that while cbhI.1 and cbhI.2 could be coregulated, cbhII can be independently controlled. The latter is so far the only cellulase gene found to be expressed when the fungus is grown on oat spelt arabinoxylan, suggesting that it may play an active role in the xylanolytic as well as the cellulolytic systems.
通过与里氏木霉cbhII基因杂交，分离出了代表黄孢原毛平革菌cbhII基因假定等位变体的两个cDNA序列。随后通过反向PCR技术分离出了两个对应的基因组序列。DNA测序表明，1380 bp的cbhII开放阅读框编码一个由460个氨基酸组成的假定多肽，该多肽被6个内含子打断。在里氏木霉cbhII中发现的结构域结构在黄孢原毛平革菌的相应蛋白质中是保守的。这两种基因产物之间的总体相似性为54%，在纤维素结合结构域中保守性最高的区域为65%。与黄孢原毛平革菌的cbhI基因不同，cbhII似乎不是一类密切相关基因的成员。CBHII是β-1,4-葡聚糖酶B家族的一个新成员。黄孢原毛平革菌和里氏木霉CBHII蛋白质序列的比对表明，对于催化结构域延伸环形成重要的所有残基以及参与里氏木霉酶催化作用的那些残基在黄孢原毛平革菌的相应序列中也存在。黄孢原毛平革菌中cbh基因的表达谱显示，虽然cbhI.1和cbhI.2可以被共同调节，但cbhII可以独立控制。到目前为止，后者是在该真菌以燕麦阿拉伯木聚糖为生长底物时发现的唯一表达的纤维素酶基因，这表明它可能在木聚糖分解系统和纤维素分解系统中都发挥积极作用。
