Support is requested for a continuation of this laboratory's structural studies of staphylococcal nuclease. In the current grant period the structures of the wild-type enzyme, and of a ternary complex of it with Ca2+ and with the nucleotide inhibitor 3',5'-deoxy-thymidine bisphosphate have been refined at high resolution to crystallographic R-values well below 0.18, forming the basis for the study of many mutant crystals; highlights are listed. The structure of the key catalytic mutant Glu-43- >Asp has been determined and refined. The structure of the mutant Val-66- >Lys has also been solved. Uniquely, this lysine is fully buried in a hydrophobic cavity. Solution studies of this mutant have allowed determination of the free energy needed to bury a charge, and of the dielectric constant within a protein. Studies of a mutant in which alanine is placed between residues 126 and 127 in the terminal helix reveal that the insertion is accommodated by a unique bulge or alpha-aneurism. Finally, in collaboration with Albert Mildvan, the structure of nuclease complexed with an authentic substrate dTpdA, and with the inactive ion La3+ has been determined by NMR and computer-assisted docking. Current specific aims focus on two areas: folding/stability and catalysis. Key catalytic studies include structure determinations of complexes of nuclease with the transition-state analogue vanadate+thymidine, and with La3+ and dTpdA. The mutant des-44-49, in which a flexible loop adjacent to the active site has been deleted appears to have a much more rigid active site, and forms the basis of proposed studies to determine why certain ions are active and others not. Stability studies will also include extension of the Val-66->Lys work to hyper-stable forms of nuclease in which the solution studies can be carried out over a wider range of conditions. Work will also proceed on a series of single and double insertion mutants placed at many sites in the molecule, and on a highly unstable quadruple mutant, known as tet 3, Data on tet 3 are being collected at a series of temperatures, in the hope that regions whose mobility increases rapidly with temperature will be revealed. A series of computational experiments is also planned.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM036358-07
Application #
3290173
Study Section
Biophysical Chemistry Study Section (BBCB)
Project Start
1986-12-01
Project End
1996-06-30
Budget Start
1993-07-01
Budget End
1994-06-30
Support Year
7
Fiscal Year
1993
Total Cost
Indirect Cost
Name
Johns Hopkins University
Department
Type
Schools of Medicine
DUNS #
045911138
City
Baltimore
State
MD
Country
United States
Zip Code
21218
Garcia-Moreno, B; Dwyer, J J; Gittis, A G et al. (1997) Experimental measurement of the effective dielectric in the hydrophobic core of a protein. Biophys Chem 64:211-24
Green, S M; Gittis, A G; Meeker, A K et al. (1995) One-step evolution of a dimer from a monomeric protein. Nat Struct Biol 2:746-51
Loll, P J; Quirk, S; Lattman, E E et al. (1995) X-ray crystal structures of staphylococcal nuclease complexed with the competitive inhibitor cobalt(II) and nucleotide. Biochemistry 34:4316-24
Abeygunawardana, C; Weber, D J; Gittis, A G et al. (1995) Solution structure of the MutT enzyme, a nucleoside triphosphate pyrophosphohydrolase. Biochemistry 34:14997-5005
Libson, A M; Gittis, A G; Lattman, E E (1994) Crystal structures of the binary Ca2+ and pdTp complexes and the ternary complex of the Asp21-->Glu mutant of staphylococcal nuclease. Implications for catalysis and ligand binding. Biochemistry 33:8007-16
Keefe, L J; Quirk, S; Gittis, A et al. (1994) Accommodation of insertion mutations on the surface and in the interior of staphylococcal nuclease. Protein Sci 3:391-401
Weber, D J; Serpersu, E H; Gittis, A G et al. (1993) NMR docking of the competitive inhibitor thymidine 3',5'-diphosphate into the X-ray structure of staphylococcal nuclease. Proteins 17:20-35
Keefe, L J; Sondek, J; Shortle, D et al. (1993) The alpha aneurism: a structural motif revealed in an insertion mutant of staphylococcal nuclease. Proc Natl Acad Sci U S A 90:3275-9
Gittis, A G; Stites, W E; Lattman, E E (1993) The phase transition between a compact denatured state and a random coil state in staphylococcal nuclease is first-order. J Mol Biol 232:718-24
Weber, D J; Gittis, A G; Mullen, G P et al. (1992) NMR docking of a substrate into the X-ray structure of staphylococcal nuclease. Proteins 13:275-87

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