NMR assignments for the amino-terminal residues of trp repressor and their role in DNA binding

The trp repressor of Escherichia coli specifically binds to operator DNAs in three operons involved in tryptophan metabolism. The NMR spectra of repressor and a chymotryptic fragment lacking the six amino-terminal residues are compared. Two-dimensional J-correlated spectra of the two forms of the pr...

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Bibliographic Details
Published in:Biochemistry (Easton) 1989-05, Vol.28 (9), p.3875-3879
Main Authors: Arrowsmith, Cheryl H, Carey, Jannette, Treat-Clemons, Lynda, Jardetzky, Oleg
Format: Article
Language:English
Subjects:
550201 - Biochemistry- Tracer Techniques
AMINO ACIDS
AROMATICS
AZAARENES
AZOLES
BACTERIA
Bacterial Proteins
BASIC BIOLOGICAL SCIENCES
CARBOXYLIC ACIDS
CHEMICAL SHIFT
Chymotrypsin
DICHROISM
DNA
DNA, Bacterial - metabolism
ESCHERICHIA COLI
Escherichia coli - genetics
Escherichia coli - metabolism
GENE OPERONS
GENE REPRESSORS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INDOLES
MAGNETIC RESONANCE
Magnetic Resonance Spectroscopy - methods
METABOLISM
MICROORGANISMS
MOLECULAR STRUCTURE
NUCLEAR MAGNETIC RESONANCE
NUCLEIC ACIDS
NUCLEOPROTEINS
Operon
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
Peptide Fragments - isolation & purification
Protein Conformation
PROTEINS
PYRROLES
Repressor Proteins - metabolism
RESONANCE
TRANSCRIPTION
Transcription Factors - metabolism
TRYPTOPHAN
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Summary:The trp repressor of Escherichia coli specifically binds to operator DNAs in three operons involved in tryptophan metabolism. The NMR spectra of repressor and a chymotryptic fragment lacking the six amino-terminal residues are compared. Two-dimensional J-correlated spectra of the two forms of the protein are superimposable except for cross-peaks that are associated with the N-terminal region. The chemical shifts and relaxation behavior of the N-terminal resonances suggest mobile "arms". Spin-echo experiments on a ternary complex of repressor with L-tryptophan and operator DNA indicate that the termini are also disordered in the complex, although removal of the arms reduces the DNA binding energy. Relaxation measurements on the armless protein show increased mobility for several residues, probably due to helix fraying in the newly exposed N-terminal region. DNA binding by the armless protein does not reduce the mobility of these residues. Thus, it appears that the arms serve to stabilize the N-terminal helix but that this structural role does not explain their contribution to the DNA binding energy. These results suggest that the promiscuous DNA binding by the arms seen in the X-ray crystal structure is found in solution as well.
ISSN:0006-2960
1520-4995
DOI:10.1021/bi00435a037