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BMC Plant Biol. 2008 Nov 27;8:120. doi: 10.1186/1471-2229-8-120.

Arabidopsis At5g39790 encodes a chloroplast-localized, carbohydrate-binding, coiled-coil domain-containing putative scaffold protein.

Author information

  • 1Department of Biological Sciences and Alberta Ingenuity Center for Carbohydrate Science, University of Calgary, Calgary, Alberta, Canada. lohmeier@ucalgary.ca

Abstract

BACKGROUND:

Starch accumulation and degradation in chloroplasts is accomplished by a suite of over 30 enzymes. Recent work has emphasized the importance of multi-protein complexes amongst the metabolic enzymes, and the action of associated non-enzymatic regulatory proteins. Arabidopsis At5g39790 encodes a protein of unknown function whose sequence was previously demonstrated to contain a putative carbohydrate-binding domain.

RESULTS:

We here show that At5g39790 is chloroplast-localized, and binds starch, with a preference for amylose. The protein persists in starch binding under conditions of pH, redox and Mg(+2) concentrations characteristic of both the day and night chloroplast cycles. Bioinformatic analysis demonstrates a diurnal pattern of gene expression, with an accumulation of transcript during the light cycle and decline during the dark cycle. A corresponding diurnal pattern of change in protein levels in leaves is also observed. Sequence analysis shows that At5g39790 has a strongly-predicted coiled-coil domain. Similar analysis of the set of starch metabolic enzymes shows that several have strong to moderate coiled-coil potential. Gene expression analysis shows strongly correlated patterns of co-expression between At5g39790 and several starch metabolic enzymes.

CONCLUSION:

We propose that At5g39790 is a regulatory scaffold protein, persistently binding the starch granule, where it is positioned to interact by its coiled-coil domain with several potential starch metabolic enzyme binding-partners.

PMID:
19038037
[PubMed - indexed for MEDLINE]
PMCID:
PMC2653042
Free PMC Article

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