4OKD

Crystal Structure of Chlamydomonas reinhardtii Isoamylase 1 (ISA1) in complex with maltoheptaose

Summary for 4OKD

• Entry DOI: 10.2210/pdb4okd/pdb
• Related PRD ID: PRD_900009
• Descriptor: Isoamylase, alpha-D-glucopyranose-(1-4)-alpha-D-glucopyranose-(1-4)-alpha-D-glucopyranose-(1-4)-alpha-D-glucopyranose-(1-4)-alpha-D-glucopyranose-(1-4)-alpha-D-glucopyranose-(1-4)-alpha-D-glucopyranose, alpha-D-glucopyranose-(1-4)-alpha-D-glucopyranose-(1-4)-alpha-D-glucopyranose, ... (5 entities in total)
• Functional Keywords: gh13 glycoside hydrolase, hydrolase
• Biological source: Chlamydomonas reinhardtii
• Total number of polymer chains: 2
• Total formula weight: 190108.78

Authors

Sim, L.,Palcic, M. (deposition date: 2014-01-22, release date: 2014-07-02, Last modification date: 2023-09-20)

Primary citation

Sim, L.,Beeren, S.R.,Findinier, J.,Dauvillee, D.,Ball, S.G.,Henriksen, A.,Palcic, M.M.
Crystal Structure of the Chlamydomonas Starch Debranching Enzyme Isoamylase ISA1 Reveals Insights into the Mechanism of Branch Trimming and Complex Assembly.
J.Biol.Chem., 289:22991-23003, 2014

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.

PubMed: 24993830
DOI: 10.1074/jbc.M114.565044

Experimental method

X-RAY DIFFRACTION (2.4 Å)