CRYSTAL STRUCTURE OF CTP-LIGATED T STATE ASPARTATE TRANSCARBAMOYLASE AT 2.5 ANGSTROMS RESOLUTION: IMPLICATIONS FOR ATCASE MUTANTS AND THE MECHANISM OF NEGATIVE COOPERATIVITY
Crystal structure of CTP-ligated T state aspartate transcarbamoylase at 2.5 A resolution: implications for ATCase mutants and the mechanism of negative cooperativity.
The X-ray crystal structure of CTP-ligated T state aspartate transcarbamoylase has been refined to an R factor of 0.182 at 2.5 A resolution using the computer program X-PLOR. The structure contains 81 sites for solvent and has rms deviations from ide ...
The X-ray crystal structure of CTP-ligated T state aspartate transcarbamoylase has been refined to an R factor of 0.182 at 2.5 A resolution using the computer program X-PLOR. The structure contains 81 sites for solvent and has rms deviations from ideality in bond lengths and bond angles of 0.018 A and 3.722 degrees, respectively. The cytosine base of CTP interacts with the main chain carbonyl oxygens of rTyr-89 and rIle-12, the main chain NH of rIle-12, and the amino group of rLys-60. The ribose hydroxyls form polar contacts with the amino group of rLys-60, a carboxylate oxygen of rAsp-19, and the main chain carbonyl oxygen of rVal-9. The phosphate oxygens of CTP interact with the amino group of rLys-94, the hydroxyl of rThr-82, and an imidazole nitrogen of rHis-20. Recent mutagenesis experiments evaluated in parallel with the structure reported here indicate that alterations in the hydrogen bonding environment of the side chain of rAsn-111 may be responsible for the homotropic behavior of the pAR5 mutant of ATCase. The location of the first seven residues of the regulatory chain has been identified for the first time in a refined ATCase crystal structure, and the proximity of this portion of the regulatory chain to the allosteric site suggests a potential role for these residues in nucleotide binding to the enzyme. Finally, a series of amino acid side chain rearrangements leading from the R1 CTP allosteric to the R6 CTP allosteric site has been identified which may constitute the molecular mechanism of distinct CTP binding sites on ATCase.
Related Citations:
Nucleotide Sequence of the Structural Gene (Pyrb) that Encodes the Catalytic Polypeptide of Aspartate Transcarbamoylase of Escherichia Coli Hoover, T.A.,Roof, W.D.,Foltermann, K.F.,O'Donovan, G.A.,Bencini, D.A.,Wild, J.R. (1983) Proc.Natl.Acad.Sci.USA 80: 2462
Structural Consequences of Effector Binding to the T State of Aspartate Carbamoyltransferase: Crystal Structures of the Unligated and ATP-and Ctp-Complexed Enzymes at 2.6 Angstroms Resolution Stevens, R.C.,Gouaux, J.E.,Lipscomb, W.N. (1990) Biochemistry 29: 7691
Structural Asymmetry in the Ctp-Liganded Form of Aspartate Carbamoyltransferase from Escherichia Coli Kim, K.H.,Pan, Z.,Honzatko, R.B.,Ke, H.-M.,Lipscomb, W.N. (1987) J.Mol.Biol. 196: 853
Amino Acid Sequence of the Catalytic Subunit of Aspartate Transcarbamoylase from Escherichia Coli Konigsberg, W.H.,Henderson, L. (1983) Proc.Natl.Acad.Sci.USA 80: 2467
Location of Amino Acid Alterations in Mutants of Aspartate Transcarbamoylase: Structural Aspects of Interallelic Complementation Schachman, H.K.,Pauza, C.D.,Navre, M.,Karels, M.J.,Wu, L.,Yang, Y.R. (1984) Proc.Natl.Acad.Sci.USA 81: 115
Organizational Affiliation:
Department of Chemistry, Gibbs Chemical Laboratory, Harvard University, Cambridge, Massachusetts 02138.
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