Plant and Cell Physiology Advance Access published online on October 11, 2007
Plant and Cell Physiology, doi:10.1093/pcp/pcm133
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Sucrose synthase oligomerization and F-actin association is regulated by sucrose concentration and phosphorylation
1Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, IL. 61801 U.S.A.
2Program in Physiological and Molecular Plant Biology, University of Illinois at Urbana-Champaign, Urbana, IL. 61801 U.S.A.
3United States Department of Agriculture-Agricultural Research Service, Photosynthesis Research Unit and Department of Crop Sciences, University of Illinois Urbana Champaign, Urbana, IL. 61801 U.S.A.
Corresponding author: Steven C. Huber, United States Department of Agriculture-Agricultural Research Service, Photosynthesis Research Unit, University of Illinois, Departments of Plant Biology and Crop Sciences, Edward R. Madigan Laboratory (ERML) Room 197, 1201 West Gregory Drive Urbana, IL 61801 USA, e-mail: schuber1{at}life.uiuc.edu, Fax: 217 244 4419, Phone: 217 265 0909
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Abstract |
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Sucrose synthase (SUS) is a key enzyme in plant metabolism, as it serves to cleave the photosynthetic end product sucrose into UDP-glucose and fructose. SUS is generally assumed to be a tetrameric protein, but results in the present study suggest that SUS can form dimers as well as tetramers and that sucrose may be a regulatory factor for the oligomerization status of SUS. The oligomerization of SUS may also affect the cellular localization of the protein. We show that sucrose concentration modulates the ability of SUS1 to associate with F-actin in vitro and that CDPK-mediated phosphorylation of recombinant SUS1 at the Ser-15 site is a negative regulator of its association with actin. Although high sucrose concentrations and hyperphosphorylation have been shown to promote SUS association with the plasma membrane (Hardin et al. 2006, Plant Physiol. 141: 1106-1119), we show that the opposite is true for the SUS: actin association. We also show that SUS1 has a unique 28 residue coiled-coil domain that does not appear to play a role in oligomerization, but may prove to be significant in the future for interactions of SUS with other proteins. Collectively, these results highlight the multifaceted nature of SUS association with cellular structures.
(Received September 2, 2007; Accepted October 8, 2007)
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