aah1 (O74922) - S. pombe 4-alpha-glucanotransferase - Review Notes

Gene Identity

• UniProt: O74922 (AGLT1_SCHPO)
• Gene: aah1 (SPCC757.12)
• EC: 2.4.1.25 (4-alpha-glucanotransferase)
• Family: GH13 (glycoside hydrolase family 13, alpha-amylase superfamily)

Key Literature

PMID:40668835 - Jacob et al. 2025, PNAS

"α-glucan remodeling by GH13-domain enzymes shapes fungal cell wall architecture."

This is the primary experimental paper for aah1 function. Key findings:
- Aah1 and Aah3 are GPI-anchored GH13-family enzymes that act redundantly PMID:40668835
- Double mutant (aah1Δ aah3Δ) shows severe phenotype: rounded cells, delayed division, clumping PMID:40668835
- Solid-state NMR: α-1,3-glucan drops from 44% to 11% in rigid phase of double mutant PMID:40668835
- Cell wall thickens ~4x (100 nm to 400 nm) with compensatory β-glucan increase
- Proposed function: GH13-family transglycosylases that remodel α-glucan downstream of Ags1 synthase

PMID:16751704 - Morita et al. 2006

"An alpha-amylase homologue, aah3, encodes a GPI-anchored membrane protein required for cell wall integrity and morphogenesis in S. pombe."

• Identified four alpha-amylase homologs (aah1-aah4) with GPI anchor signals PMID:16751704
• aah1 single deletion: no obvious phenotype at 30°C or 37°C
• aah3 single deletion: morphological defects, hypersensitivity to cell wall-degrading enzymes
• No starch-degrading activity detected in S. pombe - supports transglycosylase not hydrolase function
• Catalytic residue mutations in Aah3 abolished function, confirming enzymatic activity is required

Annotation Review Summary

Accepted (core)

• GO:0004134 4-alpha-glucanotransferase activity (IEA/ISS/ISO) - core MF
• GO:0009897 external side of plasma membrane (IEA) - core CC
• GO:0051278 fungal-type cell wall polysaccharide biosynthetic process (ISS)
• GO:0071940 fungal-type cell wall assembly (ISS)
• GO:0070600 fungal-type cell wall (1->3)-alpha-glucan biosynthetic process (IMP) - most specific BP
• GO:0009277 fungal-type cell wall (ISS)

Kept as non-core

• GO:0005509 calcium ion binding - structural cofactor, not primary function
• GO:0005886 plasma membrane - correct but less informative than external side

Removed

• GO:0016052 carbohydrate catabolic process - incorrect; Aah1 is a transglycosylase/biosynthetic enzyme, not catabolic

Over-annotated

• GO:0005975 carbohydrate metabolic process - too broad, redundant with specific BP terms

Key Gaps

• No direct enzymology on purified Aah1 (substrate specificity inferred from A. niger orthologs AgtA/AgtB)
• Individual contribution of aah1 vs aah3 unclear (strong phenotype only in double mutant)
• The "nonredundant" collaboration mentioned in PMID:40668835 suggests they may have distinct but overlapping substrate preferences

2026-11-01 consistency pass (with the aah3 review)

• Plasma membrane IEA: KEEP_AS_NON_CORE changed to MODIFY to GO:0009897, because the reason argued the term was too general.
• Carbohydrate metabolic process: MARK_AS_OVER_ANNOTATED changed to MODIFY to GO:0070600 (correct but general).
• Fungal-type cell wall polysaccharide biosynthetic process (ISS): ACCEPT changed to MODIFY to GO:0070600, its IMP-supported descendant, and removed from core_functions.
• Description and core function now say that the 4-alpha-glucanotransferase activity is inferred from A. niger AgtA/AgtB PMID:17496125 and has not been assayed on Aah1.
• Replaced three non-verbatim deep-research quotes with PMID quotes; fixed the beta-glucan figure (55% to 89%, not 54%) and a suggested question that called Aah1/Aah3 nonredundant with each other (they are redundant with each other and nonredundant with Ags1).