The structure of a cyanobacterial sucrose-phosphatase reveals the sugar tongs that release free sucrose in the cell.
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.
Fieulaine
Sonia
S
Institut de Biologie Structurale, Commissariat à l'Energie Atomique, Centre National de la Recherche Scientifique, Université Joseph Fourier, 38027 Grenoble Cedex 1, France.
Lunn
John E
JE
Borel
Franck
F
Ferrer
Jean-Luc
JL
D000595:Amino Acid Sequence / Q000502:physiology; D001224:Aspartic Acid / Q000378:metabolism; D001665:Binding Sites / Q000502:physiology; D002384:Catalysis; D020134:Catalytic Domain / Q000502:physiology; D018360:Crystallography, X-Ray; D004734:Energy Metabolism; D005947:Glucose / Q000378:metabolism; D008958:Models, Molecular; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D010766:Phosphorylation; D010940:Plant Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000502:physiology; D013395:Sucrose / Q000737:chemistry* / Q000378:metabolism; D046939:Synechocystis / Q000378:metabolism
D010940:Plant Proteins; D001224:Aspartic Acid; D013395:Sucrose; D010744:Phosphoric Monoester Hydrolases; D005947:Glucose