The long-term objective of this research project is to provide a molecular description of the events involved in the regulation of enzyme catalysis. The system under investigation involves the rigorously controlled assimilation of nitrogen in bacterial cells by the enzyme glutamine synthetase (GS). The activity of this enzyme is controlled by transcriptional activation, posttranslational modification and classical allosteric inhibition. An in-depth study is planned of catalysis and regulation of GS and of the enzymes that regulates its activity and genetic expression. The experimental approaches include protein chemistry, enzyme kinetics, spectroscopic techniques (EPR, NMR fluorescence) and site- directed mutagenesis.
The specific aims are: 1) to understand the control of the catalytic activity of GS by covalent adenylylation and deadenylylation of tyr-397. This modification affects the conformation of different regions of the protein and couples this regulatory signal to changes in catalytic activity. 2) To identify amino acids at the site surrounding tyr-397 of GS that is recognized by adenylyl transferase (ATase). 3) To understand how the regulatory protein PII interacts with ATase to ultimately control the adenylylation of Gs. 4) To systematically explore the catalytic mechanism of Gs by mutagenesis of amino acid residues considered to be involved in substrate binding, catalysis and regulation. 5) To construct a free-energy profile for the entire catalytic reaction for wild-type and mutant enzymes to aid in identifying the contribution to catalysis of each amino acid residue. 6) To understand the role of the n1 and n2 metal ions in electrophilic catalysis in the formation of the two intermediates, gamma-glu-P and the tetrahedral adduct formed between gamma- glu-P and NH3. 7) To study the proteins involved in the regulation of transcription of GS, viz., NRI, NRII and PII, especially how they interact with each other and with DNA.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM023529-15
Application #
3271700
Study Section
Biochemistry Study Section (BIO)
Project Start
1977-01-01
Project End
1995-02-28
Budget Start
1991-03-01
Budget End
1992-02-29
Support Year
15
Fiscal Year
1991
Total Cost
Indirect Cost
Name
Pennsylvania State University
Department
Type
Schools of Arts and Sciences
DUNS #
City
University Park
State
PA
Country
United States
Zip Code
16802
Reynaldo, L P; Villafranca, J J; Horrocks Jr, W D (1996) Investigating the effects of posttranslational adenylylation on the metal binding sites of Escherichia coli glutamine synthetase using lanthanide luminescence spectroscopy. Protein Sci 5:2532-44
Abell, L M; Schineller, J; Keck, P J et al. (1995) Effect of metal-ligand mutations on phosphoryl transfer reactions catalyzed by Escherichia coli glutamine synthetase. Biochemistry 34:16695-702
Witmer, M R; Palmieri-Young, D; Villafranca, J J (1994) Probing the catalytic roles of n2-site glutamate residues in Escherichia coli glutamine synthetase by mutagenesis. Protein Sci 3:1746-59
Alibhai, M; Villafranca, J J (1994) Kinetic and mutagenic studies of the role of the active site residues Asp-50 and Glu-327 of Escherichia coli glutamine synthetase. Biochemistry 33:682-6
Dhalla, A M; Li, B; Alibhai, M F et al. (1994) Regeneration of catalytic activity of glutamine synthetase mutants by chemical activation: exploration of the role of arginines 339 and 359 in activity. Protein Sci 3:476-81
Atkins, W M; Cader, B M; Hemmingsen, J et al. (1993) Time-resolved fluorescence and computational studies of adenylylated glutamine synthetase: analysis of intersubunit interactions. Protein Sci 2:800-13
Atkins, W M; Villafranca, J J (1992) Time-resolved fluorescence studies of tryptophan mutants of Escherichia coli glutamine synthetase: conformational analysis of intermediates and transition-state complexes. Protein Sci 1:342-55
McNemar, L S; Lin, W Y; Eads, C D et al. (1991) Terbium(III) luminescence study of the spatial relationship of tryptophan residues to the two metal ion binding sites of Escherichia coli glutamine synthetase. Biochemistry 30:3417-21
Lin, W Y; Dombrosky, P; Atkins, W M et al. (1991) Terbium(III) luminescence study of tyrosine emission from Escherichia coli glutamine synthetase. Biochemistry 30:3427-31
Abell, L M; Villafranca, J J (1991) Effect of metal ions and adenylylation state on the internal thermodynamics of phosphoryl transfer in the Escherichia coli glutamine synthetase reaction. Biochemistry 30:1413-8

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