@article {4406,
	title = {Assigning the NMR spectra of aromatic amino acids in proteins: analysis of two Ets pointed domains},
	journal = {Biochemistry and Cell Biology-Biochimie Et Biologie Cellulaire},
	volume = {76},
	number = {2-3},
	year = {1998},
	note = {ISI Document Delivery No.: 157QRTimes Cited: 11Cited Reference Count: 34},
	pages = {379-390},
	type = {Article},
	abstract = {The measurement of interproton nuclear Overhauser enhancements (NOEs) and dihedral angle restraints of aromatic amino acids is a critical step towards determining the structure of a protein. The complete assignment of the resonances from aromatic rings and the subsequent resolution and identification of their associated NOEs, however, can be a difficult task. Shown here is a strategy for assigning the H-1,C-13, and N-15 signals from the aromatic side chains of histidine, tryptophan, tyrosine, and phenylalanine using a suite of homo- and hetero-nuclear scalar and NOE correlation experiments, as well as selective deuterium isotope labelling. In addition, a comparison of NOE information obtained from homonuclear NOE spectroscopy (NOESY) and C-13-edited NOESY - heteronuclear single quantum correlation experiments indicates that high-resolution homonuclear two-dimensional NOESY spectra of selectively deuterated proteins are invaluable for obtaining distance restraints to the aromatic residues.},
	keywords = {ACTIVE-SITE, ANGLE, aromatic residue, BACKBONE H-1, C-13-LABELED PROTEINS, CHEMICAL-SHIFTS, dihedral, DNA-BINDING, HETERONUCLEAR NMR, HISTIDINE-RESIDUES, MAGNETIC-RESONANCE SPECTROSCOPY, NMR assignment, NOE, pH titration, PHENYLALANINE RESIDUES, TRANSCRIPTION FACTOR},
	isbn = {0829-8211},
	url = {<Go to ISI>://000078073600026},
	author = {Slupsky, C. M. and Gentile, L. N. and McIntosh, L. P.}
}
@article {3799,
	title = {Characterization of a buried neutral histidine residue in Bacillus circulans xylanase: NMR assignments, pH titration, and hydrogen exchange},
	journal = {Protein Science},
	volume = {5},
	number = {11},
	year = {1996},
	note = {ISI Document Delivery No.: VQ786Times Cited: 41Cited Reference Count: 63},
	month = {Nov},
	pages = {2319-2328},
	type = {Article},
	abstract = {Bacillus circulans xylanase contains two histidines, one of which (His 156) is solvent exposed, whereas the other (His 149) is buried within its hydrophobic core. His 149 is involved in a network of hydrogen bonds with an internal water and Ser 130, as well as a potential weak aromatic-aromatic interaction with Tyr 105. These three residues, and their network of interactions with the bound water, are conserved in four homologous xylanases. To probe the structural role played by His 149, NMR spectroscopy was used to characterize the histidines in BCX. Complete assignments of the H-1, C-13, and N-15 resonances and tautomeric forms of the imidazole rings were obtained from two-dimensional heteronuclear correlation experiments. An unusual spectroscopic feature of BCX is a peak near 12 ppm arising from the nitrogen bonded H-1(epsilon 2) of His 149. Due to its solvent inaccessibility and hydrogen bonding to an internal water molecule, the exchange rate of this proton (4.0 X 10(-5) s(-1) at pH* 7.04 and 30 degrees C) is retarded by > 10(6)-fold relative to an exposed histidine. The pK(a) of His 156 is unperturbed at similar to 6.5, as measured from the pH dependence of the N-15- and H-1-NMR spectra of BCX. In contrast, His 149 has a pK(a) < 2.3, existing in the neutral (NH)-H-epsilon 2 tautomeric state under all conditions examined. BCX unfolds at low pH and 30 degrees C, and thus His 149 is never protonated significantly in the context of the native enzyme. The structural importance of this buried histidine is confirmed by the destablizing effect of substituting a phenylalanine or glutamine at position 149 in BCX.},
	keywords = {ACTIVE-SITE, ALPHA-HELICES, AQUEOUS-SOLUTION, CHEMICAL-SHIFTS, ESCHERICHIA-COLI, GLYCOSYL HYDROLASES, H-1-NMR SPECTRUM, HYDROGEN-DEUTERIUM EXCHANGE, IMIDAZOLE, internal water, L-ALA-OH, NUCLEAR MAGNETIC-RESONANCE, pH titration, pK(alpha), PROTEIN HYDRATION, protein stability},
	isbn = {0961-8368},
	url = {<Go to ISI>://A1996VQ78600018},
	author = {Plesniak, L. A. and Connelly, G. P. and Wakarchuk, W. W. and McIntosh, L. P.}
}
