title: Arabidopsis At5g39790 encodes a chloroplast-localized, carbohydrate-binding, coiled-coil domain-containing putative scaffold protein.
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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Biological Sciences and Alberta Ingenuity Center for Carbohydrate Science, University of Calgary, Calgary, Alberta, Canada. lohmeier@ucalgary.ca
authors.forename: Elke M
authors.initials: EM
authors.lastname: Lohmeier-Vogel
authors.forename: David
authors.initials: D
authors.lastname: Kerk
authors.forename: Mhairi
authors.initials: M
authors.lastname: Nimick
authors.forename: Susan
authors.initials: S
authors.lastname: Wrobel
authors.forename: Lori
authors.initials: L
authors.lastname: Vickerman
authors.forename: Douglas G
authors.initials: DG
authors.lastname: Muench
authors.forename: Greg B G
authors.initials: GB
authors.lastname: Moorhead
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D003001:Cloning, Molecular; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D011485:Protein Binding; D016415:Sequence Alignment; D013213:Starch / Q000378:metabolism*; D013379:Substrate Specificity; D013997:Time Factors
chemical_list: D029681:Arabidopsis Proteins; D013213:Starch