Goto M, Furukawa K, Hayashida S
Department of Agricultural Chemistry, Kyushu University, Fukuoka, Japan.
Biosci Biotechnol Biochem. 1992 Oct;56(10):1523-8. doi: 10.1271/bbb.56.1523.
A single form of exo-type cellulase (Exo I; MW, 65,000), purified from a Trichoderma viride protease-depressed mutant, HK-75, digested Avicel to cellobiose exowise, and hydrolyzed cellotriose, cellotetraose, and cellopentaose in the strict manner of splitting off by cellobiose units. Exo I, however, hydrolyzed cellohexaose by both cellobiose and cellotriose units. Exo I was proteolyzed by papain into two fragments; GPExo (MW, 9,000) and Exo I' (MW, 56,000). The GPExo intensively adsorbed onto Avicel but did not hydrolyze it. Exo I' had nearly identical activity to that of intact Exo I toward cellooligosaccharides but was almost inert to Avicel in digestion and adsorption. Sequence analysis of N-terminal and C-terminal amino acids showed that GPExo was between Gly435 and Leu496 and Exo I' between Glu1 and Gly434 in Exo I. Exo I therefore consists of two domains, one for adsorption to Avicel, as demonstrated by the Avicel-affinity site, GPExo and the other for the cleavage of glycosidic linkages as demonstrated in Exo I'.
从绿色木霉蛋白酶抑制突变体HK-75中纯化得到的单一形式的外切型纤维素酶（外切酶I；分子量65,000），以外切方式将微晶纤维素消化为纤维二糖，并以严格按纤维二糖单位逐个裂解的方式水解纤维三糖、纤维四糖和纤维五糖。然而，外切酶I通过纤维二糖和纤维三糖单位水解纤维六糖。外切酶I被木瓜蛋白酶蛋白水解成两个片段：GPExo（分子量9,000）和外切酶I'（分子量56,000）。GPExo强烈吸附在微晶纤维素上但不水解它。外切酶I'对纤维寡糖的活性与完整的外切酶I几乎相同，但在消化和吸附方面对微晶纤维素几乎无活性。对N端和C端氨基酸的序列分析表明，在Exo I中，GPExo位于Gly435和Leu496之间，外切酶I'位于Glu1和Gly434之间。因此，外切酶I由两个结构域组成，一个用于吸附微晶纤维素，如由微晶纤维素亲和位点GPExo所证明，另一个用于糖苷键的裂解，如在外切酶I'中所证明。
