Alpha-amylase (AmyE) is a secreted glycosyl hydrolase family 13 (GH13) enzyme that catalyzes the endohydrolysis of (1->4)-alpha-D-glucosidic linkages in starch and related alpha-glucans. The enzyme uses a retaining double-displacement mechanism with a catalytic nucleophile (Asp217) and proton donor (Glu249). AmyE is a calcium-dependent enzyme that binds two Ca2+ ions per subunit, which are essential for structural stability and optimal catalytic activity. The protein is synthesized as a 659 amino acid precursor with an N-terminal signal peptide (residues 1-27) and propeptide (residues 28-41) that are cleaved during secretion via the Sec pathway. The mature enzyme contains a catalytic (beta/alpha)8 barrel domain (domain A) with an inserted domain B, a C-terminal beta-sandwich domain (Amy_C), and a carbohydrate-binding module (CBM26) at the C-terminus. AmyE shows activity on various starches with substrate preference potato > wheat > corn > rice, producing mainly maltose and glucose as hydrolysis products. The amyE locus is commonly used as a neutral chromosomal integration site for heterologous gene expression in B. subtilis, and the AmyE signal peptide (SPamyE) is widely used as a secretion tag for recombinant protein production.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003824 catalytic activity | IEA GO_REF:0000002 | MODIFY | Summary: AmyE is indeed a catalytic enzyme - specifically an alpha-amylase (EC 3.2.1.1) that hydrolyzes alpha-1,4-glucosidic bonds in starch. However, GO:0003824 (catalytic activity) is too general and does not provide informative annotation for this well-characterized enzyme. Reason: While the annotation is technically correct, it is uninformative. AmyE has been biochemically characterized with specific activity measurements (~1,280 U/mg), crystal structure solved (PDB:1BAG, 1UA7), and catalytic residues identified (Asp217 nucleophile, Glu249 proton donor, Asp310 transition state stabilizer). The more specific term GO:0004556 (alpha-amylase activity) should be used instead. Proposed replacements: alpha-amylase activity Supporting Evidence: UniProtKB:P00691 Reaction=Endohydrolysis of (1->4)-alpha-D-glucosidic linkages in polysaccharides containing three or more (1->4)-alpha-linked D- glucose units.; EC=3.2.1.1 |
| GO:0004556 alpha-amylase activity | IEA GO_REF:0000120 | ACCEPT | Summary: AmyE is a well-characterized alpha-amylase (EC 3.2.1.1) that catalyzes the endohydrolysis of (1->4)-alpha-D-glucosidic linkages in starch. The enzyme belongs to glycosyl hydrolase family 13 (GH13) and uses a retaining double-displacement mechanism with characterized catalytic residues (Asp217 nucleophile, Glu249 proton donor). Reason: This is the core molecular function of AmyE. The annotation is strongly supported by: (1) Crystal structure of AmyE complexed with maltopentaose showing active site architecture; (2) Enzyme classification as EC 3.2.1.1; (3) Membership in GH13 family with conserved catalytic residues; (4) Biochemical characterization showing starch hydrolysis activity producing maltose and glucose. The IEA evidence is appropriate given the computational inference from EC number and family membership, though experimental evidence also exists. Supporting Evidence: UniProtKB:P00691 RecName: Full=Alpha-amylase; EC=3.2.1.1 UniProtKB:P00691 Belongs to the glycosyl hydrolase 13 family file:BACSU/amyE/amyE-deep-research-falcon.md amyE encodes the secreted alpha-amylase of Bacillus subtilis (strain 168), a glycoside hydrolase family 13 (GH13) enzyme that hydrolyzes internal alpha-1,4-glycosidic linkages in starch and related alpha-glucans (retaining mechanism) |
| GO:0005576 extracellular region | IEA GO_REF:0000044 | ACCEPT | Summary: AmyE is a secreted enzyme that functions in the extracellular environment. The protein contains an N-terminal signal peptide (residues 1-27) and propeptide (residues 28-41) that direct secretion via the Sec pathway. Reason: This cellular component annotation is correct and represents the functional localization of AmyE. Evidence includes: (1) UniProt annotation as "Secreted"; (2) Presence of N-terminal signal peptide; (3) Direct visualization of AmyE-mCherry secretion showing discrete "secretion zones" in the cell wall (Strach et al. 2023); (4) Detection of extracellular amylase activity. The IEA inference from UniProt subcellular location vocabulary is appropriate. Supporting Evidence: UniProtKB:P00691 SUBCELLULAR LOCATION: Secreted file:BACSU/amyE/amyE-deep-research-falcon.md AmyE is exported via the Sec pathway. Strach et al. (2023) directly visualized AmyE-mCherry and observed discrete, persistent secretion zones within the Gram-positive cell wall |
| GO:0005975 carbohydrate metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: AmyE participates in carbohydrate metabolism by degrading starch, a storage polysaccharide. However, this term is quite broad and does not capture the specific biological process in which AmyE functions. Reason: While carbohydrate metabolic process is not incorrect, it is overly general for this well-characterized starch-degrading enzyme. AmyE specifically catalyzes starch hydrolysis, producing maltose and glucose. More specific terms would better represent the biological process: GO:0000272 (polysaccharide catabolic process) or GO:0009251 (glucan catabolic process) would be more informative. Proposed replacements: polysaccharide catabolic process Supporting Evidence: file:BACSU/amyE/amyE-deep-research-falcon.md Endo-acting hydrolysis of (1->4)-alpha-D-glucan linkages in starch and maltooligosaccharides, generating mainly maltose and glucose |
| GO:0016787 hydrolase activity | IEA GO_REF:0000043 | KEEP AS NON CORE | Summary: AmyE is a hydrolase enzyme that cleaves glycosidic bonds in starch. This annotation is correct but redundant with the more specific alpha-amylase activity annotation. Reason: This is a parent term of GO:0004556 (alpha-amylase activity). While technically correct, it provides less information than the specific alpha-amylase annotation. The annotation can be kept for completeness in automated inference pipelines but should not be considered a core annotation for this enzyme. Supporting Evidence: UniProtKB:P00691 3D-structure; Calcium; Carbohydrate metabolism; Glycosidase; Hydrolase |
| GO:0016798 hydrolase activity, acting on glycosyl bonds | IEA GO_REF:0000043 | KEEP AS NON CORE | Summary: AmyE acts on glycosyl bonds, specifically alpha-1,4-glucosidic linkages in starch. This annotation is more specific than general hydrolase activity but still redundant with alpha-amylase activity. Reason: This term is an intermediate parent of GO:0004556 (alpha-amylase activity) in the GO hierarchy. It is correctly assigned but provides less information than the specific alpha-amylase annotation. Keep as non-core for completeness in hierarchical inference. Supporting Evidence: UniProtKB:P00691 Belongs to the glycosyl hydrolase 13 family |
| GO:0043169 cation binding | IEA GO_REF:0000002 | MODIFY | Summary: AmyE binds calcium ions which are required for enzyme stability and activity. However, cation binding is too general - the specific cofactor is Ca2+. Reason: While AmyE does bind cations, specifically calcium ions (2 per subunit), the annotation should use the more specific term GO:0005509 (calcium ion binding). The crystal structure (PDB:1BAG) reveals specific calcium binding sites with coordinating residues identified by X-ray crystallography. Proposed replacements: calcium ion binding Supporting Evidence: UniProtKB:P00691 Name=Ca(2+); Xref=ChEBI:CHEBI:29108 UniProtKB:P00691 Binds 2 calcium ions per subunit |
| GO:0046872 metal ion binding | IEA GO_REF:0000043 | KEEP AS NON CORE | Summary: AmyE binds metal ions, specifically two calcium ions per subunit that are essential for structural stability. This annotation is correct but could be more specific. Reason: Metal ion binding is a parent term of calcium ion binding (GO:0005509). Given that the specific metal is known to be calcium (with structural evidence from X-ray crystallography), the more specific term GO:0005509 should be the core annotation. This parent term can be kept for automated inference completeness but is redundant with the specific calcium annotation. Supporting Evidence: UniProtKB:P00691 Metal-binding; Reference proteome; Secreted; Signal |
| GO:0005509 calcium ion binding | IDA file:BACSU/amyE/amyE-deep-research-falcon.md | NEW | Summary: AmyE binds two calcium ions per subunit, which are essential for enzyme stability and catalytic activity. The calcium binding sites have been determined by X-ray crystallography. Reason: This is a key molecular function of AmyE that is missing from the current annotation set. The crystal structure (PDB:1BAG, 1UA7) at 2.5 and 2.21 angstrom resolution clearly shows two calcium binding sites with specific coordinating residues. This should be annotated with experimental evidence (IDA) based on the structural characterization. Supporting Evidence: UniProtKB:P00691 Name=Ca(2+); Xref=ChEBI:CHEBI:29108 UniProtKB:P00691 Binds 2 calcium ions per subunit file:BACSU/amyE/amyE-deep-research-falcon.md Crystal structure of a catalytic-site mutant alpha-amylase from Bacillus subtilis complexed with maltopentaose |
| GO:0030247 polysaccharide binding | IDA file:BACSU/amyE/amyE-deep-research-falcon.md | NEW | Summary: AmyE binds polysaccharides (starch, maltooligosaccharides) as substrates. The enzyme contains a C-terminal carbohydrate-binding module (CBM26) and the crystal structure shows binding of maltopentaose. Reason: AmyE has been crystallized in complex with maltopentaose, demonstrating polysaccharide binding. Additionally, the protein contains a predicted CBM26 carbohydrate-binding module at the C-terminus. This binding function is essential for the enzyme's starch-degrading activity and should be annotated. Supporting Evidence: UniProtKB:P00691 CAZy; CBM26; Carbohydrate-Binding Module Family 26 file:BACSU/amyE/amyE-deep-research-falcon.md GH13 alpha-amylases possess a catalytic (beta/alpha)8 barrel (domain A) with an inserted domain B and a C-terminal beta-sandwich (Amy_C). Many Bacillus enzymes also carry carbohydrate-binding modules (CBMs) |
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Download this section (compressed HTML)Q: Are there specific regulatory mechanisms controlling amyE expression in response to starch availability?
Q: What is the precise role of the C-terminal CBM26 domain in raw starch binding and hydrolysis?
Q: How does the propeptide (residues 28-41) contribute to proper folding or secretion?
Experiment: Kinetic characterization (Km, kcat) with different starch substrates for wild-type P00691
Hypothesis: Wild-type AmyE will show substrate specificity similar to related B. subtilis alpha-amylases
Experiment: Site-directed mutagenesis of calcium-coordinating residues to assess structural vs. catalytic roles
Hypothesis: Calcium binding site mutations will differentially affect enzyme stability versus catalytic activity
Experiment: Deletion analysis of CBM26 domain to determine contribution to raw starch hydrolysis
Hypothesis: CBM26 deletion will reduce activity on raw starch substrates while maintaining activity on soluble starch
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