2dgn | pdb_00002dgn
Mouse Muscle Adenylosuccinate Synthetase partially ligated complex with GTP, 2'-deoxy-IMP
Structural highlights
Function[PURA1_MOUSE] Component of the purine nucleotide cycle (PNC), which interconverts IMP and AMP to regulate the nucleotide levels in various tissues, and which contributes to glycolysis and ammoniagenesis. Catalyzes the first committed step in the biosynthesis of AMP from IMP.[1] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedAdenylosuccinate synthetase catalyzes the first committed step in the de novo biosynthesis of AMP, coupling L-aspartate and IMP to form adenylosuccinate. Km values of IMP and 2'-deoxy-IMP are nearly identical with each substrate supporting comparable maximal velocities. Nonetheless, the Km value for L-aspartate and the Ki value for hadacidin (a competitive inhibitor with respect to L-aspartate) are 29-57-fold lower in the presence of IMP than in the presence of 2'-deoxy-IMP. Crystal structures of the synthetase ligated with hadacidin, GDP, and either 6-phosphoryl-IMP or 2'-deoxy-6-phosphoryl-IMP are identical except for the presence of a cavity normally occupied by the 2'-hydroxyl group of IMP. In the presence of 6-phosphoryl-IMP and GDP (hadacidin absent), the L-aspartate pocket can retain its fully ligated conformation, forming hydrogen bonds between the 2'-hydroxyl group of IMP and sequence-invariant residues. In the presence of 2'-deoxy-6-phosphoryl-IMP and GDP, however, the L-aspartate pocket is poorly ordered. The absence of the 2'-hydroxyl group of the deoxyribonucleotide may destabilize binding of the ligand to the L-aspartate pocket by disrupting hydrogen bonds that maintain a favorable protein conformation and by the introduction of a cavity into the fully ligated active site. At an approximate energy cost of 2.2 kcal/mol, the unfavorable thermodynamics of cavity formation may be the major factor in destabilizing ligands at the L-aspartate pocket. Cavitation as a mechanism of substrate discrimination by adenylosuccinate synthetases.,Iancu CV, Zhou Y, Borza T, Fromm HJ, Honzatko RB Biochemistry. 2006 Sep 26;45(38):11703-11. PMID:16981730[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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