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Related Experiment Video

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Transverse Sectioning of Mature Rice (Oryza sativa L.) Kernels for Scanning Electron Microscopy Imaging Using Pipette Tips as Immobilization Support

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Starch biosynthetic enzymes from developing maize endosperm associate in multisubunit complexes.

Tracie A Hennen-Bierwagen¹, Fushan Liu, Rebekah S Marsh

¹Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa 50011, USA.

Plant Physiology

|February 19, 2008

Summary

This summary is machine-generated.

This study reveals that maize starch synthases (SSs) and starch branching enzymes (BEs) physically associate in multisubunit complexes within amyloplasts, explaining their functional relationships in starch biosynthesis.

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Area of Science:

Biochemistry
Plant Biology
Molecular Genetics

Background:

Mutations in starch biosynthetic enzymes often cause pleiotropic effects, suggesting functional relationships between enzymes like starch synthases (SSs) and starch branching enzymes (BEs).
The molecular basis for these functional interactions within the starch biosynthetic pathway remains unclear.
Physical association in multisubunit complexes is a potential explanation for the observed functional relationships.

Purpose of the Study:

To investigate stable protein-protein interactions between specific maize starch synthases (SSI, SSIIa, SSIII) and starch branching enzymes (BEI, BEIIa, BEIIb).
To determine if these enzymes form stable multisubunit complexes in maize amyloplasts.

Main Methods:

In vivo protein-protein interaction tests in yeast nuclei.
Immunoprecipitation assays.
Affinity purification using recombinant proteins.
Gel permeation chromatography to assess complex molecular mass.

Main Results:

Eight instances of specific SS and BE polypeptide associations, either direct or indirect, were detected.
Direct pairwise interactions were confirmed by in vivo yeast assays.
Gel permeation chromatography revealed high molecular mass complexes (approx. 600 kD and 300 kD) containing specific SS and BE subunits.
Monomeric forms of the proteins were also detected, indicating dynamic complex formation.

Conclusions:

Maize starch synthases and starch branching enzymes physically associate in stable multisubunit complexes.
These protein-protein interactions provide a molecular explanation for the functional relationships observed between enzymes in the starch biosynthetic pathway.
The stability of these complexes at high salt concentrations suggests involvement of hydrophobic interactions in subunit association.