Faculty Collaboration Database

NMR studies of the conformations and location of nucleotides bound to the Escherichia coli MutT enzyme. Biochemistry 1995 Apr 25;34(16):5577-86

Date

04/25/1995

Pubmed ID

7727419

DOI

10.1021/bi00016a032

Scopus ID

2-s2.0-0029024156 (requires institutional sign-in at Scopus site)   45 Citations

Abstract

The MutT enzyme catalyzes the hydrolysis of nucleoside triphosphates to nucleoside monophosphates and pyrophosphate by substitution at the rarely attacked beta-phosphorus. Nucleotides containing bulky substituents at the 8 position of the purine ring are preferentially hydrolyzed. The conformation of the MutT-bound nonhydrolyzable substrate analog Mg(2+)-AMPCPP, determined by 10 intramolecular NOEs and molecular dynamics refinement using a full relaxation matrix analysis with back-calculation of the NOESY intensities, is high anti (chi = 53 +/- 9 degrees), with a C2'-exo, O1'-endo sugar pucker. Similarly, the product of dGTP hydrolysis, dGMP, also binds MutT in a high anti (chi = 73 +/- 9 degrees) C1'-endo conformation based on seven intramolecular NOEs. Such high anti rotations of the base would allow MutT to accommodate nucleotides substituted at the C-8 position with no intramolecular clashes. Changes in chemical shifts in the 1H-15N spectra of the enzyme induced by Mg2+ and Mg2+ AMPCPP suggest that the metal activator and nucleotide interact with residues in loop I, at the carboxyl end of helix I, loop II, loop III, and beta-strands A and B of the secondary structure of MutT. The displacement of Mg2+ by Mn2+ causes the selective disappearance due to paramagnetic broadening of 1H-15N cross peaks from G37, G38, and K39 in loop I and E57 in helix I. Eleven intermolecular NOEs between Mg2+AMPCPP and hydrophobic residues of MutT are found, three of which are tentatively assigned to L67 in loop II and three to L54 in helix I. Similarly, seven intermolecular NOEs between dGMP and hydrophobic residues of the enzyme are found, four of which are tentatively assigned to L54 and two to V58, both in helix I. These interactions indicate that the loop I-helix I-loop II motif contributes significantly to the active site of MutT in accord with mutagenesis studies and with sequence homologies among MutT-like NTP pyrophosphohydrolases.

Author List

Frick DN, Weber DJ, Abeygunawardana C, Gittis AG, Bessman MJ, Mildvan AS

Author

David N. Frick PhD Associate Professor in the Chimistry & Biochemistry department at University of Wisconsin - Milwaukee

MESH terms used to index this publication - Major topics in bold

Adenosine Triphosphate
Amino Acid Sequence
Bacterial Proteins
Binding Sites
Escherichia coli
Escherichia coli Proteins
Guanosine Triphosphate
Magnetic Resonance Spectroscopy
Models, Molecular
Models, Structural
Molecular Conformation
Molecular Sequence Data
Phosphoric Monoester Hydrolases
Protein Conformation
Protein Structure, Secondary
Pyrophosphatases
Sequence Homology, Amino Acid