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(2022-08-31 17:40):
Paper# www.pnas.org/cgi/doi/10.1073/pnas.1714249114 Distinct roles of N- and O-glycans in cellulase activity and stability
N-和O-聚糖在纤维素酶活性和稳定性中的独特的作用
在自然界中,许多微生物分泌糖苷水解酶,氧化还原酶,辅助的生物酶的混合物,以降解多糖衍生物和植物的木质素等。这些酶通常被糖基化修饰,通常分为N-和o -糖基化,其作用已被广泛认为是为应对细胞外的恶略的环境,防止这些生物酶被水解。糖基化修饰酶蛋白已被证明对活性成倍的影响,但这些影响尚未完全被了解。在这里,我们研究了糖苷水解酶家族7的纤维生物水解酶(Cel7A), 模拟了其的含有o -糖基化位修饰点的纤维素结合结构域,模拟了其的含有N-和o -糖基化位点的催化结构域,以及含了o -糖基化位点修饰有抑制水解功能的链接linker结构域。我们报道了纤维素酶Cel7A 糖基化修饰的共识图谱,包括糖链位点和基序。此外,我们检查糖基化修饰在降解多糖得活性、底物结合和热和蛋白水解稳定性等方面的作用。纤维生物水解酶(Cel7A)催化结构域(CD)上的N-糖基化位点被敲除后的实验结果显示,N-糖基化位点的敲除对纤维生物水解酶(Cel7A)催化活性及与纤维素底物的结合程度的影响很小, 但确实影响纤维生物水解酶(Cel7A)的稳定性。纤维素结合结构域(CBM)的O-糖基化位点的敲除,含对酶结合纤维素底物的影响并不大,对整个酶蛋白的抗外界的酶解作用,对整个酶蛋白的活性的影响都不大。然而,连接纤维素结合结构域和催化结构域的linker的o -糖基化,极大的增加了整个酶蛋白抗水解的能力。通过分子模拟预测了连接子(linker)区域的o -糖基化的附加作用,即当纤维素结合于Cel7A为在上,模型预测了α-螺旋的形成和增加了非糖基化连接子与纤维素的相互作用。总的来说,这项研究揭示了N-和o -糖基化可能的关键作用广泛适用于其他植物细胞壁降解酶。
IF:9.400Q1
Proceedings of the National Academy of Sciences of the United States of America,
2017-12-26.
DOI: 10.1073/pnas.1714249114
PMID: 29229855
Distinct roles of N- and O-glycans in cellulase activity and stability
翻译
Abstract:
In nature, many microbes secrete mixtures of glycoside hydrolases, oxidoreductases, and accessory enzymes to deconstruct polysaccharides and lignin in plants. These enzymes are often decorated with N- and O-glycosylation, the roles of which have been broadly attributed to protection from proteolysis, as the extracellular milieu is an aggressive environment. Glycosylation has been shown to sometimes affect activity, but these effects are not fully understood. Here, we examine N- and O-glycosylation on a model, multimodular glycoside hydrolase family 7 cellobiohydrolase (Cel7A), which exhibits an O-glycosylated carbohydrate-binding module (CBM) and an O-glycosylated linker connected to an N- and O-glycosylated catalytic domain (CD)-a domain architecture common to many biomass-degrading enzymes. We report consensus maps for Cel7A glycosylation that include glycan sites and motifs. Additionally, we examine the roles of glycans on activity, substrate binding, and thermal and proteolytic stability. N-glycan knockouts on the CD demonstrate that N-glycosylation has little impact on cellulose conversion or binding, but does have major stability impacts. O-glycans on the CBM have little impact on binding, proteolysis, or activity in the whole-enzyme context. However, linker O-glycans greatly impact cellulose conversion via their contribution to proteolysis resistance. Molecular simulations predict an additional role for linker O-glycans, namely that they are responsible for maintaining separation between ordered domains when Cel7A is engaged on cellulose, as models predict α-helix formation and decreased cellulose interaction for the nonglycosylated linker. Overall, this study reveals key roles for N- and O-glycosylation that are likely broadly applicable to other plant cell-wall-degrading enzymes.
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