Mannan endo-1,4-beta-mannosidase
Catalyses the random hydrolysis of (1-4)-beta-D-mannosidic linkages in mannans, galactomannans and glucomannans.
Reference Protein and Structure
- Sequence
-
Q9ZF13
(3.2.1.78)
(Sequence Homologues)
(PDB Homologues)
- Biological species
-
Thermobifida fusca (Bacteria)
- PDB
-
1bqc
- BETA-MANNANASE FROM THERMOMONOSPORA FUSCA
(1.5 Å)
- Catalytic CATH Domains
-
3.20.20.80
(see all for 1bqc)
Enzyme Reaction (EC:3.2.1.78)
+
→
Alternative enzyme names: Beta-1, 4-mannan 4-mannanohydrolase, Beta-D-mannanase, Beta-mannanase B, Endo-1,4-beta-mannanase, Endo-beta-1,4-mannase, Endo-beta-mannanase, Endo-1,4-mannanase, Beta-mannanase, 1,4-beta-D-mannan mannanohydrolase, Beta-1,4-mannan 4-mannanohydrolase,
Enzyme Mechanism
Introduction
This is a retaining mannanase, in which the glycosidic oxygen is protonated by Glu128 (proton donor) and the anomeric carbon atom is attacked by Glu225 (nucleophile). The resulting mannosyl–mannanase intermediate is then hydrolysed by a water molecule, generating a product with the same anomeric configuration as the substrate.
Catalytic Residues Roles
| UniProt | PDB* (1bqc) | ||
| His194 | His196A | Modifies the pKa of Glu128 such that it can act as the general acid/base. | modifies pKa |
| Trp252 | Trp254A | Provides a hydrophobic environment to bind and stabilise the intermediates. | activator, electrostatic stabiliser |
| Glu223 | Glu225A | Acts as the nucleophile. | covalent catalysis |
| Asn125 | Asn127A | Helps position and stabilise Arg50. It may also interact with the equatorial HO–C(2) in cellulases. Probable role in transition state stabiisation. | electrostatic stabiliser |
| Glu126 | Glu128A | Acts as the general acid/base. | proton shuttle (general acid/base) |
| Tyr196, Arg48 | Tyr198A, Arg50A | Acts to modify the pKa of Glu225, ensuring it is correctly protonated to act as the nucleophile. | modifies pKa |
*PDB label guide - RESx(y)B(C) - RES: Residue Name; x: Residue ID in PDB file;
y: Residue ID in PDB sequence if different from PDB file; B: PDB Chain;
C: Biological Assembly Chain if different from PDB. If label is "Not Found" it means this residue is not found in the reference PDB.
Chemical Components
References
- Hilge M et al. (1998), Structure, 6, 1433-1444. High-resolution native and complex structures of thermostable β-mannanase from Thermomonospora fusca – substrate specificity in glycosyl hydrolase family 5. DOI:10.1016/s0969-2126(98)00142-7. PMID:9817845.
- Kumagai Y et al. (2016), FEBS Lett, 590, 2862-2869. Molecular insights into the mechanism of thermal stability of actinomycete mannanase. DOI:10.1002/1873-3468.12322. PMID:27447091.
- Aspeborg H et al. (2012), BMC Evol Biol, 12, 186-. Evolution, substrate specificity and subfamily classification of glycoside hydrolase family 5 (GH5). DOI:10.1186/1471-2148-12-186. PMID:22992189.
- Kumagai Y et al. (2012), Biochimie, 94, 2783-2790. The structural analysis and the role of calcium binding site for thermal stability in mannanase. DOI:10.1016/j.biochi.2012.09.012. PMID:23009928.
- Tailford LE et al. (2009), Biochemistry, 48, 7009-7018. Understanding How Diverse β-Mannanases Recognize Heterogeneous Substrates. DOI:10.1021/bi900515d. PMID:19441796.
- Larsson AM et al. (2006), J Mol Biol, 357, 1500-1510. Three-dimensional Crystal Structure and Enzymic Characterization of β-Mannanase Man5A from Blue Mussel Mytilus edulis. DOI:10.1016/j.jmb.2006.01.044. PMID:16487541.
- Bourgault R et al. (2005), Protein Sci, 14, 1233-1241. Three-dimensional structure of (1,4)-β-d-mannan mannanohydrolase from tomato fruit. DOI:10.1110/ps.041260905. PMID:15840830.
- Sabini E et al. (2000), Acta Crystallogr D Biol Crystallogr, 56, 3-13. The three-dimensional structure of a Trichoderma reesei beta-mannanase from glycoside hydrolase family 5. PMID:10666621.
Catalytic Residues Roles
| Residue | Roles |
|---|---|
| Arg50A | modifies pKa |
| Tyr198A | modifies pKa |
| Glu128A | proton shuttle (general acid/base) |
| His196A | modifies pKa |
| Asn127A | electrostatic stabiliser |
| Trp254A | activator, electrostatic stabiliser |
| Glu225A | covalent catalysis |