The objective is to elucidate the control mechanisms involved in the regulation of de novo pyrimidine biosynthesis in mammalian cells. The first three enzymes of the pathway, carbamyl phosphate synthetase, aspartate transcarbamylase and dihydroorotase are carried by a single 230 Kd polypeptide chain. This large multifunctional protein, called CAD, also exhibits homotropic and heterotropic allosteric transitions. Contiguous lengths of the polypeptide chain are separately folded into globular domains having specific functions. To map the domain structure of CAD, the molecule will be cleaved by controlled proteolysis into active fragments which will be isolated by HPLC and affinity chromatography. Moreover a library of monoclonal antibodies directed against different regions of the CAD molecule will be developed for immunoaffinity chromatography and for use as structural probes. The functional sites on each fragment will be mapped by enzyme assays, binding studies and specific chemical modification. The size and juxtaposition of each domain within the polypeptide will be established by HPLC peptide mapping, partial amino acid sequencing and immunochemical methods. Most of the primary structure of CAD will be determined by nucleotide sequencing of a nearly full length cDNA molecule. The oligomeric structure of CAD and its domains, the intra and interdomain interactions and the arrangement of domains with the intact complex will be investigated by electron microscopy, chemical crosslinking and hydrodynamic methods. To identify explain the aggregate functional properties such as channelling and reduction in transient time resulting from the association of the component enzymes, steady state, pre-steady state and reconstitution studies are planned. Comparative studies of the amino acid sequence of CAD with proteins of related function but different structure, correlation of the domain structure of CAD with the fine structure of its gene, and structural comparison of CAD with mitochondrial carbamyl phosphate synthetase may give insight into the origin of CAD. This research should provide a much clearer understanding of multifunctional proteins, a recently discovered class of molecules which are likely to have an important regulatory role in mammalian cells. Moreover CAD is the major locus of control in de novo pyrimidine biosynthesis, a pathway essential for cellular proliferation, so that this work may have implications in understanding proliferative disorders.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA027674-10
Application #
3167773
Study Section
Biochemistry Study Section (BIO)
Project Start
1980-03-01
Project End
1991-06-30
Budget Start
1989-07-01
Budget End
1990-06-30
Support Year
10
Fiscal Year
1989
Total Cost
Indirect Cost
Name
Wayne State University
Department
Type
Schools of Medicine
DUNS #
City
Detroit
State
MI
Country
United States
Zip Code
48202
Bergh, S T; Evans, D R (1993) Subunit structure of a class A aspartate transcarbamoylase from Pseudomonas fluorescens. Proc Natl Acad Sci U S A 90:9818-22
Kim, H; Kelly, R E; Evans, D R (1992) The structural organization of the hamster multifunctional protein CAD. Controlled proteolysis, domains, and linkers. J Biol Chem 267:7177-84
Kim, H S; Lee, L; Evans, D R (1991) Identification of the ATP binding sites of the carbamyl phosphate synthetase domain of the Syrian hamster multifunctional protein CAD by affinity labeling with 5'-[p-(fluorosulfonyl)benzoyl]adenosine. Biochemistry 30:10322-9
Scully, J L; Evans, D R (1991) Comparative modeling of mammalian aspartate transcarbamylase. Proteins 9:191-206
Bein, K; Simmer, J P; Evans, D R (1991) Molecular cloning of a cDNA encoding the amino end of the mammalian multifunctional protein CAD and analysis of the 5'-flanking region of the CAD gene. J Biol Chem 266:3791-9
Chaparian, M G; Evans, D R (1991) The catalytic mechanism of the amidotransferase domain of the Syrian hamster multifunctional protein CAD. Evidence for a CAD-glutamyl covalent intermediate in the formation of carbamyl phosphate. J Biol Chem 266:3387-95
Simmer, J P; Kelly, R E; Rinker Jr, A G et al. (1990) Mammalian dihydroorotase: nucleotide sequence, peptide sequences, and evolution of the dihydroorotase domain of the multifunctional protein CAD. Proc Natl Acad Sci U S A 87:174-8
Simmer, J P; Kelly, R E; Rinker Jr, A G et al. (1990) Mammalian carbamyl phosphate synthetase (CPS). DNA sequence and evolution of the CPS domain of the Syrian hamster multifunctional protein CAD. J Biol Chem 265:10395-402
Simmer, J P; Kelly, R E; Scully, J L et al. (1989) Mammalian aspartate transcarbamylase (ATCase): sequence of the ATCase domain and interdomain linker in the CAD multifunctional polypeptide and properties of the isolated domain. Proc Natl Acad Sci U S A 86:4382-6
Chaparian, M G; Evans, D R (1988) Intracellular location of the multidomain protein CAD in mammalian cells. FASEB J 2:2982-9

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