3e5m
Crystal structure of the HSCARG Y81A mutant
Structural highlights
FunctionNMRL1_HUMAN Redox sensor protein. Undergoes restructuring and subcellular redistribution in response to changes in intracellular NADPH/NADP(+) levels. At low NADPH concentrations the protein is found mainly as a monomer, and binds argininosuccinate synthase (ASS1), the enzyme involved in nitric oxide synthesis. Association with ASS1 impairs its activity and reduces the production of nitric oxide, which subsecuently prevents apoptosis. Under normal NADPH concentrations, the protein is found as a dimer and hides the binding site for ASS1. The homodimer binds one molecule of NADPH. Has higher affinity for NADPH than for NADP(+). Binding to NADPH is necessary to form a stable dimer.[1] [2] [3] 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 PubMedNADP(H) is an important cofactor that controls many fundamental cellular processes. We have determined the crystal structure of HSCARG, a novel NADPH sensor, and found that it forms an asymmetrical dimer with only one subunit occupied by an NADPH molecule, and the two subunits have dramatically different conformations. To study the role of NADPH in affecting the structure and function of HSCARG, here, we constructed a series of HSCARG mutants to abolish NADPH binding ability. Protein structures of two mutants, R37A and Y81A, were solved by X-ray crystallography. The dimerization of wild-type and mutant HSCARG was studied by dynamic light scattering. Differences between the function of wild-type and mutant HSCARG were also compared. Our results show that binding of NADPH is necessary for HSCARG to form a stable asymmetric dimer. The conformation of the monomeric mutants was similar to that of NADPH-bound Molecule I in wild-type HSCARG, although some conformational changes were found in the NADPH binding site. Furthermore, we also noticed that abolition of NADPH binding ability changes the distribution of HSCARG in the cell and that these mutants without NADPH are more strongly associated with argininosuccinate synthetase as compared with wild-type HSCARG. These data suggest that NADPH functions as an allosteric regulator of the structure and function of HSCARG. In response to the changes in the NADPH/NADP(+) ratio within cells, HSCARG, as a redox sensor, associates and dissociates with NADPH to form a new dynamic equilibrium. This equilibrium, in turn, will tip the dimerization balance of the protein molecule and consequently controls the regulatory function of HSCARG. NADPH is an allosteric regulator of HSCARG.,Dai X, Li Y, Meng G, Yao S, Zhao Y, Yu Q, Zhang J, Luo M, Zheng X J Mol Biol. 2009 Apr 17;387(5):1277-85. Epub 2009 Feb 28. PMID:19254724[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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