Publications

• Purification, molecular cloning, and sequence analysis of sucrose-6F-phosphate phosphohydrolase from plants.

  Lunn J.E., Ashton A.R., Hatch M.D., Heldt H.W.

  Sucrose-6(F)-phosphate phosphohydrolase (SPP; EC ) catalyzes the final step in the pathway of sucrose biosynthesis and is the only enzyme of photosynthetic carbon assimilation for which the gene has not been identified. The enzyme was purified to homogeneity from rice (Oryza sativa L.) leaves and ... >> More

  Sucrose-6(F)-phosphate phosphohydrolase (SPP; EC ) catalyzes the final step in the pathway of sucrose biosynthesis and is the only enzyme of photosynthetic carbon assimilation for which the gene has not been identified. The enzyme was purified to homogeneity from rice (Oryza sativa L.) leaves and partially sequenced. The rice leaf enzyme is a dimer with a native molecular mass of 100 kDa and a subunit molecular mass of 50 kDa. The enzyme is highly specific for sucrose 6(F)-phosphate with a K(m) of 65 microM and a specific activity of 1250 micromol min(-1) mg(-1) protein. The activity is dependent on Mg(2+) with a remarkably low K(a) of 8-9 microM and is weakly inhibited by sucrose. Three peptides from cleavage of the purified rice SPP with endoproteinase Lys-C showed similarity to the deduced amino acid sequences of three predicted open reading frames (ORF) in the Arabidopsis thaliana genome and one in the genome of the cyanobacterium Synechocystis sp. PCC6803, as well as cDNA clones from Arabidopsis, maize, and other species in the GenBank database of expressed sequence tags. The putative maize SPP cDNA clone contained an ORF encoding a 420-amino acid polypeptide. Heterologous expression in Escherichia coli showed that this cDNA clone encoded a functional SPP enzyme. The 260-amino acid N-terminal catalytic domain of the maize SPP is homologous to the C-terminal region of sucrose-phosphate synthase. A PSI-BLAST search of the GenBank database indicated that the maize SPP is a member of the haloacid dehalogenase hydrolase/phosphatase superfamily. << Less

  Proc. Natl. Acad. Sci. U.S.A. 97:12914-12919(2000) [PubMed] [EuropePMC]

• New complexities in the synthesis of sucrose.

  Lunn J.E., MacRae E.

  Sucrose is universal in plants and fulfils many roles: transport sugar, storage reserve, compatible solute and signal compound. Consequently, sucrose synthesis is highly regulated, with much of the control operating at the first step in the committed pathway, which is catalysed by sucrose-phosphat ... >> More

  Sucrose is universal in plants and fulfils many roles: transport sugar, storage reserve, compatible solute and signal compound. Consequently, sucrose synthesis is highly regulated, with much of the control operating at the first step in the committed pathway, which is catalysed by sucrose-phosphate synthase (SPS). The discovery of at least three SPS gene families in plants has added a further layer of complexity to an already complicated picture involving transcriptional, allosteric and post-translational control of this enzyme's activity. After years of neglect, the gene encoding the last enzyme in the pathway, sucrose-phosphatase (SPP), has finally been cloned, revealing that SPS contains an SPP-like domain at the carboxy-terminus, to which SPP might bind. This has reinvigorated the search for an SPS-SPP complex, and has hinted at further complexities to be unravelled in the control of sucrose synthesis in plants. << Less

  Curr Opin Plant Biol 6:208-214(2003) [PubMed] [EuropePMC]

• The structure of a cyanobacterial sucrose-phosphatase reveals the sugar tongs that release free sucrose in the cell.

  Fieulaine S., Lunn J.E., Borel F., Ferrer J.L.

  Sucrose-phosphatase (SPP) catalyzes the final step in the pathway of sucrose biosynthesis in both plants and cyanobacteria, and the SPPs from these two groups of organisms are closely related. We have crystallized the enzyme from the cyanobacterium Synechocystis sp PCC 6803 and determined its crys ... >> More

  Sucrose-phosphatase (SPP) catalyzes the final step in the pathway of sucrose biosynthesis in both plants and cyanobacteria, and the SPPs from these two groups of organisms are closely related. We have crystallized the enzyme from the cyanobacterium Synechocystis sp PCC 6803 and determined its crystal structure alone and in complex with various ligands. The protein consists of a core domain containing the catalytic site and a smaller cap domain that contains a glucose binding site. Two flexible hinge loops link the two domains, forming a structure that resembles a pair of sugar tongs. The glucose binding site plays a major role in determining the enzyme's remarkable substrate specificity and is also important for its inhibition by sucrose and glucose. It is proposed that the catalytic reaction is initiated by nucleophilic attack on the substrate by Asp9 and involves formation of a covalent phospho-Asp9-enzyme intermediate. From modeling based on the SPP structure, we predict that the noncatalytic SPP-like domain of the Synechocystis sucrose-phosphate synthase could bind sucrose-6(F)-phosphate and propose that this domain might be involved in metabolite channeling between the last two enzymes in the pathway of sucrose synthesis. << Less

  Plant Cell 17:2049-2058(2005) [PubMed] [EuropePMC]