The long-term objective of this project is to develop a total view of how succinyl-CoA synthetase (SCS) is assembled and how it functions catalytically. In the present application, two lines of approach are proposed. First, site-directed mutagenesis will be performed with the alpha2 beta2 SCS from E. coli, in order to change amino acid residues that are known or strongly suggested to be involved at the active site. The initial residues to be examined are a reactive sulfhydryl group on the Beta-subunit and histidine-246 of the alpha-subunit, site of compulsory phosphorylation during the enzymatic reaction. Three tryptophan residues on the beta-subunit will also be subjected to mutation, in order to explain inactivation of SCS by chemical modification. Plasmid GS131 which contains the genes for the alpha- and Beta- subunits of E. coli SCS will be mutagenized in vitro using oligonucleotides that contain single or double base mismatches. The E. coli deletion strain TK3D18 which does not contain SCS will be transformed with the mutant plasmids. The enzyme protein will be isolated using adaptations of the established purification procedure for the wild type protein. Kinetic analyses will be performed, in order to characterize the type of effect, if any, the mutation has had on the enzyme. It is expected that mutation of alphahis-246 to asn will lower kcat significantly. Chemical derivatives of the alpha-subunit will be prepared and isolated. They will be used to test the alternating sites cooperativity model that has been proposed for this enzyme. The second approach will involve study of the refolding of E. coli SCS and SCS from pig heart, which is an alpha beta protein. The dependency of the refolding of E. coli SCS on ATP will be studied by molecular exclusion in an HPLC system and the use of fluorescent probes. Pig heart SCS which has only recently been observed to refold to give active enzyme for the first time will be examined by circular dichroism spectroscopy in guanidine hydrochloride solutions, as well as by the use of HPLC and fluorescent probes. It will be of interest to determine why the pig heart enzyme does not require nucleoside triphosphate substrate for activation upon refolding.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM017534-20
Application #
3269133
Study Section
Pathobiochemistry Study Section (PBC)
Project Start
1978-09-01
Project End
1992-08-31
Budget Start
1990-09-01
Budget End
1991-08-31
Support Year
20
Fiscal Year
1990
Total Cost
Indirect Cost
Name
University of Texas Health Science Center San Antonio
Department
Type
Schools of Medicine
DUNS #
800772162
City
San Antonio
State
TX
Country
United States
Zip Code
78229
Nishimura, J S; Ybarra, J; Mann, C J et al. (1993) Sensitivity of Escherichia coli succinyl-CoA mutants at Trp beta 76 to clostripain and to trypsin. ADP and ATP protect against cleavage by clostripain at Arg beta 80. J Biol Chem 268:13717-22
Luo, G X; Nishimura, J S (1992) Adenosine 5'-tetraphosphate is synthesized by the histidine alpha 142----asparagine mutant of Escherichia coli succinyl-CoA synthetase. J Biol Chem 267:9516-20
Mann, C J; Mitchell, T; Nishimura, J S (1991) Phosphorylation and formation of hybrid enzyme species test the ""half of sites"" reactivity of Escherichia coli succinyl-CoA synthetase. Biochemistry 30:1497-503
Luo, G X; Nishimura, J S (1991) Site-directed mutagenesis of Escherichia coli succinyl-CoA synthetase. Histidine 142 alpha is a facilitative catalytic residue. J Biol Chem 266:20781-5
Nishimura, J S; Mann, C J; Ybarra, J et al. (1990) Intrinsic fluorescence of succinyl-CoA synthetase and four tryptophan mutants. Tryptophan 76 and tryptophan 248 of the beta-subunit are responsive to CoA binding. Biochemistry 29:862-5
Mann, C J; Hardies, S C; Nishimura, J S (1989) Site-directed mutagenesis of Escherichia coli succinyl-CoA synthetase. beta-Cys325 is a nonessential active site residue. J Biol Chem 264:1457-60
Khan, I A; Nishimura, J S (1988) Native-like intermediate on the folding pathway of Escherichia coli succinyl-CoA synthetase. J Biol Chem 263:2152-8
Nishimura, J S; Ybarra, J; Mitchell, T et al. (1988) Isolation, amino acid analyses and refolding of subunits of pig heart succinyl-CoA synthetase. Biochem J 250:429-34
Ybarra, J; Prasad, A R; Nishimura, J S (1986) Chemical modification of tryptophan residues in Escherichia coli succinyl-CoA synthetase. Effect on structure and enzyme activity. Biochemistry 25:7174-8
Nishimura, J S; Mitchell, T (1985) Reaction of substrates with 35S-thiophosphorylated succinyl-CoA synthetase of pig heart. Similarities to the case of the Escherichia coli enzyme. J Biol Chem 260:2077-9