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Biochemical and structural insights into a thermostable cellobiohydrolase from Myceliophthora thermophila
Author(s) -
Kadowaki Marco A. S.,
Higasi Paula,
Godoy Mariana O.,
Prade Rolf A.,
Polikarpov Igor
Publication year - 2018
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/febs.14356
Subject(s) - computational biology , biology , biochemistry , chemistry
Cellobiohydrolases hydrolyze cellulose, a linear polymer with glucose monomers linked exclusively by β‐1,4 glycosidic linkages. The widespread hydrogen bonding network tethers individual cellulose polymers forming crystalline cellulose, which prevent the access of hydrolytic enzymes and water molecules. The most abundant enzyme secreted by Myceliophthora thermophila M77 in response to the presence of biomass is the cellobiohydrolase Mt Cel7A, which is composed by a GH 7‐catalytic domain ( CD ), a linker, and a CBM 1‐type carbohydrate‐binding module. GH 7 cellobiohydrolases have been studied before, and structural models have been proposed. However, currently available GH 7 crystal structures only define separate catalytic domains and/or cellulose‐binding modules and do not include the full‐length structures that are involved in shaping the catalytic mode of operation. In this study, we determined the 3D structure of catalytic domain using X‐ray crystallography and retrieved the full‐length enzyme envelope via small‐angle X‐ray scattering ( SAXS ) technique. The SAXS data reveal a tadpole‐like molecular shape with a rigid linker connecting the CD and CBM . Our biochemical studies show that Mt Cel7A has higher catalytic efficiency and thermostability as well as lower processivity when compared to the well‐studied Tr Cel7A from Trichoderma reesei . Based on a comparison of the crystallographic structures of CD s and their molecular dynamic simulations, we demonstrate that Mt Cel7A has considerably higher flexibility than Tr Cel7A. In particular, loops that cover the active site are more flexible and undergo higher conformational fluctuations, which might account for decreased processivity and enhanced enzymatic efficiency. Our statistical coupling analysis suggests co‐evolution of amino acid clusters comprising the catalytic site of Mt Cel7A, which correlate with the steps in the catalytic cycle of the enzyme. Database The atomic coordinates and structural factors of Mt Cel7A have been deposited in the Protein Data Bank with accession number 5W11.