Plant and Cell Physiology Advance Access originally published online on October 11, 2007
Plant and Cell Physiology 2007 48(11):1612-1623; doi:10.1093/pcp/pcm133
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Sucrose Synthase Oligomerization and F-actin Association are Regulated by Sucrose Concentration and Phosphorylation
1Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
2Program in Physiological and Molecular Plant Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
3United States Department of Agriculture-Agricultural Research Service, Photosynthesis Research Unit and Department of Crop Sciences, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
*Corresponding author: E-mail, schuber1{at}life.uiuc.edu; Fax, +1-217-244-4419.
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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 calcium-dependent protein kinase-mediated phosphorylation of recombinant SUS1 at the Ser15 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, 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.
Keywords: Sucrose synthase - F-actin binding - protein oligomerization - calcium dependent protein kinase - protein phosphorylation - sugar sensing
Abbreviations: AEBSF, 4-(aminoethyl)benzenesulfonyl fluoride hydrochloride; CD, circular dichroism; CDPK, calcium-dependent protein kinase; DAP, days after pollination; DTT, dithiothreitol; PBST, phosphate-buffered saline containing 0.1% (v/v) Tween-20; MBP, maltose-binding protein; MCLR, microcystin-LR; PVPP, polyvinylpolypyrrolidone; SUS, sucrose synthase; TFE, 2,2,2-trifluoroethanol.
(Received September 2, 2007; Accepted October 8, 2007)
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