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Crystal structure of a chitinase (RmChiA) from the thermophilic fungus Rhizomucor miehei with a real active site tunnel. 2021

Zhengqiang Jiang, and Songqing Hu, and Junwen Ma, and Yuchun Liu, and Zhu Qiao, and Qiaojuan Yan, and Yonggui Gao, and Shaoqing Yang
College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China.

A chitinase gene (RmChiA) encoding 445 amino acid (aa) residues from a fungus Rhizomucor miehei was cloned and overexpressed in Escherichia coli. Two kinds of RmChiA crystal forms, with space groups P32 2 1 and P1, were obtained by sitting-drop vapor diffusion and the structures were determined by X-ray diffraction. The overall structure of RmChiA monomer, which is the first structure of bacterial-type chitinases from nonpathogenic fungi, adopts a canonical triosephosphate isomerase (TIM) barrel fold with two protruding chitinase insertion domains. RmChiA exhibited a unique NxDxE catalytical motif and a real active site tunnel structure, which are firstly found in GH family 18 chitinases. The motif had high structural homolog with the typical DxDxE motif in other GH family 18 chitinases. The tunnel is formed by two unusual long loops, containing 15 aa and 45 aa respectively, linked by a disulfide bond across the substrate-binding cleft. Mutation experiments found that opening the roof of tunnel structure increased the hydrolysis efficiency of RmChiA, but the thermostability of the mutants decreased. Moreover, the tunnel structure endowed RmChiA with the exo-chitinase character.

UI MeSH Term Description Entries
D009154 Mutation Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations. Mutations
D002688 Chitinases Glycoside hydrolases that break down glycosidic bonds in CHITIN. They are important for insect and worm morphogenesis and plant defense against pathogens. Human chitinases may play a role in the etiology of allergies and asthma. Chitinase,Endochitinase
D004795 Enzyme Stability The extent to which an enzyme retains its structural conformation or its activity when subjected to storage, isolation, and purification or various other physical or chemical manipulations, including proteolytic enzymes and heat. Enzyme Stabilities,Stabilities, Enzyme,Stability, Enzyme
D005656 Fungal Proteins Proteins found in any species of fungus. Fungal Gene Products,Fungal Gene Proteins,Fungal Peptides,Gene Products, Fungal,Yeast Proteins,Gene Proteins, Fungal,Peptides, Fungal,Proteins, Fungal
D006868 Hydrolysis The process of cleaving a chemical compound by the addition of a molecule of water.
D020103 Rhizomucor A genus of zygomycetous fungi of the family Mucoraceae, order MUCORALES. Rhizomucors
D020134 Catalytic Domain The region of an enzyme that interacts with its substrate to cause the enzymatic reaction. Active Site,Catalytic Core,Catalytic Region,Catalytic Site,Catalytic Subunit,Reactive Site,Active Sites,Catalytic Cores,Catalytic Domains,Catalytic Regions,Catalytic Sites,Catalytic Subunits,Core, Catalytic,Cores, Catalytic,Domain, Catalytic,Domains, Catalytic,Reactive Sites,Region, Catalytic,Regions, Catalytic,Site, Active,Site, Catalytic,Site, Reactive,Sites, Active,Sites, Catalytic,Sites, Reactive,Subunit, Catalytic,Subunits, Catalytic

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