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- PDB-9j6x: Cryo-EM structure of the rice isoamylase ISA1-ISA2 heterocomplex -

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Basic information

Entry
Database: PDB / ID: 9j6x
TitleCryo-EM structure of the rice isoamylase ISA1-ISA2 heterocomplex
Components
  • Isoamylase 1, chloroplastic
  • Isoamylase 2, chloroplastic
KeywordsHYDROLASE / isoamylase ISA1-ISA2
Function / homology
Function and homology information


chloroplast isoamylase complex / isoamylase complex / isoamylase / isoamylase activity / amylopectin biosynthetic process / starch biosynthetic process / starch catabolic process / chloroplast
Similarity search - Function
Isoamylase 2, catalytic domain / : / Isoamylase 1-3, C-terminal / Glycogen debranching enzyme GlgX/isoamylase, N-terminal Early set domain / Glycoside hydrolase, family 13, N-terminal / Carbohydrate-binding module 48 (Isoamylase N-terminal domain) / Alpha amylase, catalytic domain / Glycosyl hydrolase, family 13, catalytic domain / Alpha-amylase domain / Glycosyl hydrolase, all-beta ...Isoamylase 2, catalytic domain / : / Isoamylase 1-3, C-terminal / Glycogen debranching enzyme GlgX/isoamylase, N-terminal Early set domain / Glycoside hydrolase, family 13, N-terminal / Carbohydrate-binding module 48 (Isoamylase N-terminal domain) / Alpha amylase, catalytic domain / Glycosyl hydrolase, family 13, catalytic domain / Alpha-amylase domain / Glycosyl hydrolase, all-beta / Immunoglobulin E-set / Glycoside hydrolase superfamily / Immunoglobulin-like fold
Similarity search - Domain/homology
Isoamylase 1, chloroplastic / Isoamylase 2, chloroplastic
Similarity search - Component
Biological speciesOryza sativa Japonica Group (Japanese rice)
MethodELECTRON MICROSCOPY / single particle reconstruction / cryo EM / Resolution: 2.4 Å
AuthorsGuan, Z.Y. / Yan, J.J.
Funding support China, 1items
OrganizationGrant numberCountry
National Natural Science Foundation of China (NSFC) China
CitationJournal: Nat Commun / Year: 2025
Title: Amylopectin branch trimming and biosynthesis elucidated by the rice isoamylase ISA1-ISA2 heterocomplex.
Authors: Rong Fan / Zeyuan Guan / Guanghong Zhou / Xi Yang / Fei Zhang / Menglong Wu / Xuecui Wang / Jian Liu / Pei Chen / Yanjun Liu / Delin Zhang / Ping Yin / Junjie Yan /
Abstract: Amylopectin, the primary form of starch in plant leaves, seeds and tubers, features a tree-like architecture with branched glucose chains. Excess branches result in the formation of soluble ...Amylopectin, the primary form of starch in plant leaves, seeds and tubers, features a tree-like architecture with branched glucose chains. Excess branches result in the formation of soluble phytoglycogen instead of starch granules. In higher plants and green algae, the debranching enzyme isoamylase ISA1 forms either homomultimer or hetero-multimer with ISA2 to facilitate branch trimming and starch granule formation, but the molecular basis remains largely unknown. In this study, we reconstitute the rice OsISA1-ISA2 complex in vitro and determine the cryo-EM structures of the OsISA1 homodimer, as well as the malto-oligosaccharide (MOS)-free and MOS-bound OsISA1-ISA2 heterocomplex. The OsISA1 dimer shows a tail-to-tail rod-like architecture, whereas the OsISA1-ISA2 complex mainly exhibits as a trimer, with OsISA2 flanking on the N-terminal segments of the dimeric OsISA1. Combined with comprehensive biochemical analyses, these structural data elucidate the organization of the ISA1-ISA2 heterocomplex in higher plants and demonstrate how ISA1 and ISA2 cooperate during amylopectin biosynthesis.
History
DepositionAug 17, 2024Deposition site: PDBJ / Processing site: PDBC
Revision 1.0May 28, 2025Provider: repository / Type: Initial release
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Revision 1.2Jul 23, 2025Group: Data collection / Category: em_admin / em_software / Item: _em_admin.last_update / _em_software.name
Revision 1.1Jul 23, 2025Data content type: EM metadata / Data content type: EM metadata / EM metadata / Group: Data processing / Experimental summary / Data content type: EM metadata / EM metadata / Category: em_admin / em_software / Data content type: EM metadata / EM metadata / Item: _em_admin.last_update / _em_software.name

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Structure visualization

Structure viewerMolecule:
MolmilJmol/JSmol

Downloads & links

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Assembly

Deposited unit
A: Isoamylase 1, chloroplastic
B: Isoamylase 1, chloroplastic
C: Isoamylase 2, chloroplastic


Theoretical massNumber of molelcules
Total (without water)261,1853
Polymers261,1853
Non-polymers00
Water00
1


  • Idetical with deposited unit
  • defined by author
  • Evidence: electron microscopy, not applicable
TypeNameSymmetry operationNumber
identity operation1_5551

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Components

#1: Protein Isoamylase 1, chloroplastic / OsISA1 / Protein SUGARY-1


Mass: 87281.594 Da / Num. of mol.: 2
Source method: isolated from a genetically manipulated source
Source: (gene. exp.) Oryza sativa Japonica Group (Japanese rice)
Gene: ISA1, ISA, SU1, Os08g0520900, LOC_Os08g40930 / Production host: Escherichia coli BL21(DE3) (bacteria) / References: UniProt: D0TZF0, isoamylase
#2: Protein Isoamylase 2, chloroplastic / OsISA2


Mass: 86622.008 Da / Num. of mol.: 1
Source method: isolated from a genetically manipulated source
Source: (gene. exp.) Oryza sativa Japonica Group (Japanese rice)
Gene: ISA2, Os05g0393700, LOC_Os05g32710, OsJ_17304, OSJNBa0014C03.3
Production host: Escherichia coli BL21(DE3) (bacteria) / References: UniProt: Q6AU80, isoamylase
Has protein modificationN

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Experimental details

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Experiment

ExperimentMethod: ELECTRON MICROSCOPY
EM experimentAggregation state: PARTICLE / 3D reconstruction method: single particle reconstruction

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Sample preparation

ComponentName: SA1-ISA2 heterocomplex / Type: COMPLEX / Entity ID: all / Source: RECOMBINANT
Source (natural)Organism: Oryza sativa Japonica Group (Japanese rice)
Source (recombinant)Organism: Escherichia coli BL21(DE3) (bacteria)
Buffer solutionpH: 8
SpecimenConc.: 0.6 mg/ml / Embedding applied: NO / Shadowing applied: NO / Staining applied: NO / Vitrification applied: YES
VitrificationCryogen name: ETHANE

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Electron microscopy imaging

Experimental equipment
Model: Titan Krios / Image courtesy: FEI Company
MicroscopyModel: TFS KRIOS
Electron gunElectron source: FIELD EMISSION GUN / Accelerating voltage: 300 kV / Illumination mode: FLOOD BEAM
Electron lensMode: BRIGHT FIELD / Nominal defocus max: 1600 nm / Nominal defocus min: 1200 nm
Image recordingElectron dose: 50 e/Å2 / Film or detector model: GATAN K3 BIOQUANTUM (6k x 4k)

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Processing

EM softwareName: PHENIX / Category: model refinement
CTF correctionType: NONE
SymmetryPoint symmetry: C1 (asymmetric)
3D reconstructionResolution: 2.4 Å / Resolution method: FSC 0.143 CUT-OFF / Num. of particles: 148552 / Symmetry type: POINT
RefinementHighest resolution: 2.4 Å
Stereochemistry target values: REAL-SPACE (WEIGHTED MAP SUM AT ATOM CENTERS)
Refine LS restraints
Refine-IDTypeDev idealNumber
ELECTRON MICROSCOPYf_bond_d0.00317463
ELECTRON MICROSCOPYf_angle_d0.50123712
ELECTRON MICROSCOPYf_dihedral_angle_d4.5352358
ELECTRON MICROSCOPYf_chiral_restr0.0432466
ELECTRON MICROSCOPYf_plane_restr0.0043110

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