Abstract
Sucrose transport is the central system for the allocation of carbon resources in vascular plants. During growth and development, plants control carbon distribution by coordinating sites of sucrose synthesis and cleavage in different plant organs and different cellular locations. Sucrose synthase, which reversibly catalyzes sucrose synthesis and cleavage, provides a direct and reversible means to regulate sucrose flux. Depending on the metabolic environment, sucrose synthase alters its cellular location to participate in cellulose, callose, and starch biosynthesis through its interactions with membranes, organelles, and cytoskeletal actin. The x-ray crystal structure of sucrose synthase isoform 1 from Arabidopsis thaliana (AtSus1) has been determined as a complex with UDP-glucose and as a complex with UDP and fructose, at 2.8- and 2.85-Å resolutions, respectively. The AtSus1 structure provides insights into sucrose catalysis and cleavage, as well as the regulation of sucrose synthase and its interactions with cellular targets.
Highlights
Sucrose flux in plants is partly achieved through sucrose synthesis and cleavage catalyzed by sucrose synthase
Depending on the metabolic environment, sucrose synthase alters its cellular location to participate in cellulose, callose, and starch biosynthesis through its interactions with membranes, organelles, and cytoskeletal actin
sucrose synthase (SUS) participates in the regulation of sucrose flux by rapidly altering its cellular location from the cytosol to sites of cellulose, callose, and starch biosynthesis (7, 20 –22), and through its interaction with various organelle membranes [4, 23, 24] and cytoskeletal actin [25, 26]
Summary
Sucrose flux in plants is partly achieved through sucrose synthesis and cleavage catalyzed by sucrose synthase. The x-ray crystal structure of sucrose synthase isoform 1 from Arabidopsis thaliana (AtSus1) has been determined as a complex with UDP-glucose and as a complex with UDP and fructose, at 2.8- and 2.85-Aresolutions, respectively. The AtSus structure provides insights into sucrose catalysis and cleavage, as well as the regulation of sucrose synthase and its interactions with cellular targets. SUS participates in the regulation of sucrose flux by rapidly altering its cellular location from the cytosol to sites of cellulose, callose, and starch biosynthesis (7, 20 –22), and through its interaction with various organelle membranes [4, 23, 24] and cytoskeletal actin [25, 26]. The SUS1 isoform from A. thaliana (AtSus1) has the primary sequence structure of a typical sucrose synthase: residues 1 to 276 form an N-terminal “regulatory” domain involved in cellu-. The structure of AtSus highlighted features that may be involved in SUS regulation by phosphorylation, thiolation, and its interaction with cellular targets
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