Design and synthesis of peptides that bind alpha-bungarotoxin with high affinity

BACKGROUND: Alpha-bungarotoxin (alpha-BTX) is a highly toxic snake venom alpha-neurotoxin that binds to acetylcholine receptor (AChR) at the neuromuscular junction, and is a potent inhibitor of this receptor. We describe the design and synthesis of peptides that bind alpha-BTX with high affinity, and inhibit its interaction with AChR with an IC(50) of 2 nM. The design of these peptides was based on a lead peptide with an IC(50) of 3x10(-7) M, previously identified by us [M. Balass et al., Proc. Natl. Acad. Sci. USA 94 (1997) 6054] using a phage-display peptide library. RESULTS: Employing nuclear magnetic resonance-derived structural information [T. Scherf et al., Proc. Natl. Acad. Sci. USA 94 (1997) 6059] of the complex of alpha-BTX with the lead peptide, as well as structure-function analysis of the ligand-binding site of AChR, a systematic residue replacement of the lead peptide, one position at a time, yielded 45 different 13-mer peptides. Of these, two peptides exhibited a one order of magnitude increase in inhibitory potency in comparison to the lead peptide. The design of additional peptides, with two or three replacements, resulted in peptides that exhibited a further increase in inhibitory potency (IC(50) values of 2 nM), that is more than two orders of magnitude better than that of the original lead peptide, and better than that of any known peptide derived from AChR sequence. The high affinity peptides had a protective effect on mice against alpha-BTX lethality. CONCLUSIONS: Synthetic peptides with high affinity to alpha-BTX may be used as potential lead compounds for developing effective antidotes against alpha-BTX poisoning. Moreover, the procedure employed in this study may serve as a general approach for the design and synthesis of peptides that interact with high affinity with any desired biological target.     

Crystal structures of phenyl-substituted cyclopropanes. IV. the crystal structure (at 21‡C and −100‡C) and the phenyl ring conformation in 4-cyclopropylacetanilide

The crystal structure of 4-cyclopropylacetanilide was investigated at room temperature (21C) and at –100C in order to determine the orientation of the phenyl ring with respect to the cyclopropane moiety and the effect of this substituent on the stereochemistry of the three-membered ring. The compound was chosen because it is one of the few species containing a simple phenyl ring as the sole cyclopropane ring substituent and whose crystals are suitable for X-ray diffraction at room temperature. The substance crystallizes in space groupP2_l/c at either temperature (no phase transitions) with cell constants: (at 21C)a=9.725(2),b=10.934(3), andc=9.636(2) å,=106.13(1);V=984.21 å³ andd(calc;z=4)=1.182 g cm^–3. The relevant parameters for the –100C structure area=9.557(4),b=10.980(2), andc=9.641(2) å,=106.34(3);V=970.76 å³ and d(calc;z=4)=1.199 g cm^–3. Final values wereR(F)=0.042, R_w=0.035, using unit weights, and its nonhydrogen atoms were used to phase the low-temperature data, whose final discrepancy indices wereR(F)=0.051,R _w =0.061. The phenyl substituent is almost exactly in the bisecting conformation with respect to the C-C-C angle at the point of attachment to cyclopropane and conjugative effects are clearly evident in the lengths of the cyclopropane ring [1.494(3), 1.498(3), and 1.474(4) å, the later being the distal bond]. If one omits the terminal methylene fragments at C10 and C11, the atoms comprising the acetanilide fragment and the substituted carbon of the cyclopropane ring lie in a nearly perfect plane. Molecular mechanics as well as semiempirical (AM1) calculations were carried out in order to determine the structure of the energy-minimized configurations in the two computational environments. The molecular conformations thus obtained are close to that experimentally observed from the X-ray diffraction experiment. In both theoretical models, the lowest energy conformation is that in which the plane of the phenyl ring bisects the cyclopropane C-C-C angle as was experimentally observed. Finally, the shape of the conformational barrier as a function of the orientation of the plane of the phenyl ring was computed, giving a maximum barrier to rotation of 2.2 kcal/mol. Similar calculations were carried out for two other aryl cyclopropanes, whose rings (naphthalene and anthracene) cannot adopt the bisecting position. Comparisons of experimental geometrical parameters as well as of the barriers to rotation are presented.on leave at the University of Houston, 1995–1996.     

The Photochemical and Thermal Interconversion of Some Cyclopentadienone Dimers

In continuation of previous work on cyclopentadienone dimers [3], thermal and photochemical interconversions of the isomeric diketones 1, 3 , and 5 by skeletal rearrangements have been established to the extent summarized in schemes 2 and 3, and the intramolecular [2+2] cycloaddition 1 → 2 was found to be reversible photochemically.     

Hypersurfaces of prescribed mean curvature enclosing a given body

Given a smooth domain Ω in ℝ ^m+1 with compact closure and a smooth integrable functionh: ℝ ^m+1→ℝ satisfyingh(x)≥H _∂Ω (x) on ∂Ω whereH _∂ω denotes the mean curvature of ∂Ω calculated w.r.t. the interior unit normal we show that there is a setA⊂ℝ ^m+1 with the properties andH _∂A=h on ∂A.     

β relaxation theory for simple systems: some addenda

The evolution of the tagged particle probability density for a hard sphere system is evaluated within the -relaxation window. Relaxation curves obtained by molecular dynamics studies by Barrat, Hansen and Roux for a binary mixture are analyzed quantitatively with -relaxation scaling formulae. The dynamical light scattering data obtained by Pusey and van Megen for colloidal suspensions are described by the combined - and -relaxation scaling results. The range of validity of asymptotic expressions near a glass transition singularity is discussed for the Debye-Waller factor as a function of packing fraction. The applied theoretical formulae are those of the mode coupling theory for the liquid to glass transition.