NMR spectroscopy combined with paramagnetic relaxation agents was used to study the positioning of the 40-residue Alzheimer Amyloid beta-peptide Abeta(1-40) in SDS micelles. 5-Doxyl stearic acid incorporated into the micelle or Mn(2+) ions in the aqueous solvent were used to determine the position of the peptide relative to the micelle geometry. In SDS solvent, the two alpha-helices induced in Abeta(1-40), comprising residues 15-24, and 29-35, respectively, are surrounded by flexible unstructured regions. NMR signals from these unstructured regions are strongly attenuated in the presence of Mn(2+) showing that these regions are positioned mostly outside the micelle. The central helix (residues 15-24) is significantly affected by 5-doxyl stearic acid however somewhat less for residues 16, 20, 22 and 23. This alpha-helix therefore resides in the SDS headgroup region with the face with residues 16, 20, 22 and 23 directed away from the hydrophobic interior of the micelle. The C-terminal helix is protected both from 5-doxyl stearic acid and Mn(2+), and should be buried in the hydrophobic interior of the micelle. The SDS micelles were characterized by diffusion and (15)N-relaxation measurements. Comparison of experimentally determined translational diffusion coefficients for SDS and Abeta(1-40) show that the size of SDS micelle is not significantly changed by interaction with Abeta(1-40).

Given that oral rehydration is less invasive than IV rehydration with no evidence of important clinical differences, it is the first choice for rehydration in children with AGE and mild-to-moderate dehydration. As the vast majority of children with AGE do not require IV rehydration, oral ondansetron administration to children with significant vomiting should be performed to reduce the use of IV rehydration and the need for hospital admission. In children deemed too unwell to receive oral rehydration therapy, IV ondansetron administration is an option, as its use is associated with lower hospital admission rates. Although probiotics appear to be an effective option for the treatment of AGE amongst hospitalized children, outpatient data is lacking and more studies are urgently needed to determine the optimal organism, dosing and duration of treatment.

The solution structure of Ca 2+ -bound regulatory domain of cardiac troponin C (cNTnC) in complex with the switch region of troponin I (cTnI [147][148][149][150][151][152][153][154][155][156][157][158][159][160][161][162][163] ) and the calmodulin antagonist, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfinamide (W7), has been determined by NMR spectroscopy. The structure reveals that the W7 naphthalene ring interacts with the terminal methyl groups of M47, M60, and M81 as well as aliphatic and aromatic side-chains of several other residues in the hydrophobic pocket of cNTnC. The H3 ring proton of W7 also contacts the methyl groups of I148 and M153 of cTnI [147][148][149][150][151][152][153][154][155][156][157][158][159][160][161][162][163] . The N-(6-aminohexyl) tail interacts primarily with the methyl groups of V64 and M81, which are located on the C-and D-helices of cNTnC. Compared to the structure of the cNTnC•Ca 2+ •W7 complex (Hoffman, R. M. B. and Sykes, B. D. (2009) Biochemistry 48, 5541-5552), the tail of W7 reorients slightly towards the surface of cNTnC while the ring remains in the hydrophobic pocket. The positively charged -NH 3 + group from the tail of W7 repels the positively charged R147 of cTnI [147][148][149][150][151][152][153][154][155][156][157][158][159][160][161][162][163] . As a result, the N-terminus of the peptide moves away from cNTnC and the helical content of cTnI [147][148][149][150][151][152][153][154][155][156][157][158][159][160][161][162][163] is diminished, when compared to the structure of cNTnC•Ca 2+ •cTnI [147][148][149][150][151][152][153][154][155][156][157][158][159][160][161][162][163] (Li, M. X., Spyracopoulos, L., and Sykes B. D. (1999) Biochemistry 38, 8289-8298). Thus the ternary structure cNTnC•Ca 2+ •W7•cTnI [147][148][149][150][151][152][153][154][155][156][157][158][159][160][161][162][163] reported in this study offers an explanation for the ∼13-fold affinity reduction of cTnI [147][148][149][150][151][152][153][154][155][156][157][158][159][160][161][162][163] for cNTnC•Ca 2+ in the presence of W7, and provides a structural basis for the inhibitory effect of W7 in cardiac muscle contraction. This generates molecular insight into structural features that are useful for the design of cTnC-specific Ca 2+ -desensitizing drugs. Keywordstroponin; structure; drugs; mechanism; inhibition A healthy human heart generates ∼3 billion contractile cycles over an average life span. Each contractile cycle involves systolic activation and diastolic relaxation, regulated by Ca 2+ association and dissociation from troponin in the cardiac myofilaments. Troponin is a *To whom correspondence should be addressed. Phone Number: (780) 492-5460, Fax Number: (780) 492-0886, brian.sykes@ualberta.ca. Data Deposition: The atomic coordinates have been deposited in the RCSB Protein Data Bank (PDB accession code: 2KRD) Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early ve...

It is not certain whether the helix propagation parameters s(n)() (i.e., the equilibrium constants between (n - 1)- and n-residue long alpha-helices) determined from numerous studies of rather long model peptides are applicable for description of the initial steps of the helix formation during the protein folding process. From fluorescence, NMR, and calorimetric studies of a series of model peptides, containing the La(3+)-binding sequence nucleating the helix (Siedlecka, M., Goch, G., Ejchart, A., Sticht, H., and Bierzynski, A. (1999) Proc. Natl. Acad. Sci. U.S.A. 96, 903-908), we have determined, at 25 degrees C, the average values of the enthalpy DeltaH(n)() and of the helix growth parameters s(n)() describing the first four steps of helix propagation in polyalanine. The absolute values of the C-cap parameters, describing the contribution of the C-terminal residues to the helix free energy, have also been estimated for alanine (1.2 +/- 0.5) and NH(2) group (1.6 +/- 0.7). The initial four steps of the helix growth in polyalanine can be described by a common propagation parameter s = 1.54 +/- 0.04. The enthalpy DeltaH(n)() is also constant and equals -980 +/- 100 cal mol(-)(1).