Extracellular Aldonolactonase from Myceliophthora thermophila
Extracellular Aldonolactonase from Myceliophthora thermophila
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DOI：
10.1128/aem.01922-10
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发表时间：
2011-01-01
影响因子：
4.4
通讯作者：
Marletta, Michael A.
中科院分区：
文献类型：
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作者：
Beeson, William T.;Iavarone, Anthony T.;Marletta, Michael A.
真菌分泌许多不同的酶来分解木质纤维生物质，包括几个水解酶家族、氧化酶和许多未知的蛋白质。在这里，我们描述了从嗜热真菌Myceliopthora thermophila(同名为Sporotrichum thermophile)中分离、鉴定和初步序列分析的胞外醛内酯酶。该酶是一种大小为48 kDa的糖蛋白，具有广泛的最适pH。该酶催化葡萄糖基-三角洲-内酯和纤维二酮-三角洲-内酯的水解，在pH 5.0和25℃时，其表观二级速率常数k(Cat)/K-m与1×10(6)M-1 S(-1)相近，但不能水解木-γ-内酯和阿拉伯-γ-内酯。序列分析表明，该酶与某些细菌中存在的顺式-羧基-变酸内酯酶(CMLE)和6-磷酸葡萄糖内酯酶有较远的同源性。嗜热支原体基因组包含两个预测的胞外内酰胺酶基因，这两个基因的表达都是在纯纤维素存在下诱导的。嗜热支原体内酯酶的同源物也被预测为胞外，几乎存在于所有已知的纤维分解子囊菌中。
Fungi secrete many different enzymes to deconstruct lignocellulosic biomass, including several families of hydrolases, oxidative enzymes, and many uncharacterized proteins. Here we describe the isolation, characterization, and primary sequence analysis of an extracellular aldonolactonase from the thermophilic fungus Myceliophthora thermophila (synonym Sporotrichum thermophile). The lactonase is a 48-kDa glycoprotein with a broad pH optimum. The enzyme catalyzes the hydrolysis of glucono-delta-lactone and cellobiono-delta-lactone with an apparent second-order rate constant, k(cat)/K-m, of similar to 1 x 10(6) M-1 s(-1) at pH 5.0 and 25 degrees C but is unable tohydrolyze xylono-gamma-lactone or arabino-gamma-lactone. Sequence analyses of the lactonase show that it has distant homology to cis-carboxy-muconate lactonizing enzymes (CMLE) as well as 6-phosphogluconolactonases present in some bacteria. The M. thermophila genome contains two predicted extracellular lactonase genes, and expression of both genes is induced by the presence of pure cellulose. Homologues of the M. thermophila lactonase, which are also predicted to be extracellular, are present in nearly all known cellulolytic ascomycetes.