Crystal Structure of Chlamydomonas reinhardtii Isoamylase 1 (ISA1)

Experimental Data Snapshot

  • Resolution: 2.30 Å
  • R-Value Free: 0.235 
  • R-Value Work: 0.202 
  • R-Value Observed: 0.203 

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This is version 1.4 of the entry. See complete history


Crystal Structure of the Chlamydomonas Starch Debranching Enzyme Isoamylase ISA1 Reveals Insights into the Mechanism of Branch Trimming and Complex Assembly.

Sim, L.Beeren, S.R.Findinier, J.Dauvillee, D.Ball, S.G.Henriksen, A.Palcic, M.M.

(2014) J Biol Chem 289: 22991-23003

  • DOI: https://doi.org/10.1074/jbc.M114.565044
  • Primary Citation of Related Structures:  
    4J7R, 4OKD

  • PubMed Abstract: 

    The starch debranching enzymes isoamylase 1 and 2 (ISA1 and ISA2) are known to exist in a large complex and are involved in the biosynthesis and crystallization of starch. It is suggested that the function of the complex is to remove misplaced branches of growing amylopectin molecules, which would otherwise prevent the association and crystallization of adjacent linear chains. Here, we investigate the function of ISA1 and ISA2 from starch producing alga Chlamydomonas. Through complementation studies, we confirm that the STA8 locus encodes for ISA2 and sta8 mutants lack the ISA1·ISA2 heteromeric complex. However, mutants retain a functional dimeric ISA1 that is able to partly sustain starch synthesis in vivo. To better characterize ISA1, we have overexpressed and purified ISA1 from Chlamydomonas reinhardtii (CrISA1) and solved the crystal structure to 2.3 Å and in complex with maltoheptaose to 2.4 Å. Analysis of the homodimeric CrISA1 structure reveals a unique elongated structure with monomers connected end-to-end. The crystal complex reveals details about the mechanism of branch binding that explains the low activity of CrISA1 toward tightly spaced branches and reveals the presence of additional secondary surface carbohydrate binding sites.

  • Organizational Affiliation

    Carlsberg Laboratory, Gamle Carlsberg Vej 10, DK-1799 Copenhagen V, Denmark and. Electronic address: lya.sim@gmail.com.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
A, B
840Chlamydomonas reinhardtiiMutation(s): 0 
Gene Names: Isa1
Find proteins for Q7X8Q2 (Chlamydomonas reinhardtii)
Explore Q7X8Q2 
Go to UniProtKB:  Q7X8Q2
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupQ7X8Q2
Sequence Annotations
  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Resolution: 2.30 Å
  • R-Value Free: 0.235 
  • R-Value Work: 0.202 
  • R-Value Observed: 0.203 
  • Space Group: P 41 21 2
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 102.13α = 90
b = 102.13β = 90
c = 488.63γ = 90
Software Package:
Software NamePurpose
XSCALEdata scaling
PDB_EXTRACTdata extraction
XDSdata reduction

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2014-03-19
    Type: Initial release
  • Version 1.1: 2014-07-02
    Changes: Database references
  • Version 1.2: 2014-07-23
    Changes: Database references
  • Version 1.3: 2014-09-03
    Changes: Database references
  • Version 1.4: 2023-09-20
    Changes: Data collection, Database references, Refinement description