SUCROSE SYNTHASE (SUS) OLIGOMERIZATION IS REGULATED BY SUCROSE LEVELS WITHIN PLANT CELLS

Authors: DUNCAN, KATERI - UNIVERSITY OF ILLINOIS; HARDIN, SHANE - UNIVERSITY OF ILLINOIS; Huber, Steven

Submitted to: American Society of Plant Biologists
Publication Type: Abstract Only
Publication Acceptance Date: 3/1/2006
Publication Date: 7/1/2006
Citation: Duncan, K.A., Hardin, S., Huber, S.C. 2006. Sucrose synthase (SUS) oligomerization is regulated by sucrose levels within plant cells [abstract]. American Society of Plant Biologists. Abstract no. P24012. Available: http://abstracts.aspb.org/pb2006/public/P24/P24012.html.

Interpretive Summary:

Technical Abstract: Sucrose synthase (SUS) is an important plant metabolic enzyme as it cleaves sucrose in the cytoplasm of plant cells. There are three known isoforms of SUS within Zea mays: SUS1, SUS-SH1, and SUS2 (formerly SUS3). It is thought that SUS is predominantly a hetero-tetramer composed of the three isoforms. However, recent evidence suggests that in developing maize kernels, SUS-SH1 is a homo-oligomer, while SUS1 and SUS2 can form hetero-oligomers. Using size exclusion chromatography of a maize kernel extract as well as a recombinant maltose-binding protein tagged (MBP) SUS1, we demonstrate that SUS1 oligomerization is affected by sucrose. In the presence of sucrose both native and recombinant protein approaches show that SUS1 forms a tetramer, while in the absence of sucrose SUS1 elutes as a dimer/trimer. SUS-SH1 native protein also shows an oligomeric shift from a tetramer to a dimer in the absence of sucrose; SUS2, however, does not show a shift in elution volume. This sucrose-dependent oligomerization could be a new component of sucrose sensing in vivo. The SUS1 isoform has a putative coiled-coil region that we show by recombinant truncation analysis is not involved in oligomerization status. SUS is predominantly cytoplasmic, however it can associate with the plasma membrane to shuttle UDP-glucose into cellulose synthesis. Recent evidence using membrane co-sedimentation assays with a series of C-terminal truncations of recombinant SUS1 indicates that the extreme N-terminus is required for membrane association. Further studies to evaluate several binding capabilities, including elucidation of the oliogmerization domain within SUS1, are underway.