ISSN:
1075-2617
Keywords:
β-turns
;
folded conformation
;
dehydro-residue
;
X-ray diffraction
;
consecutive dehydro-residue
;
Chemistry
;
Biochemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
To obtain general rules of peptide design using α,β-dehydro-residues, a sequence with two consecutive ΔPhe-residues, Boc-L-Val-ΔPhe-ΔPhe- L-Ala-OCH3, was synthesized by azlactone method in solution phase. The peptide was crystallized from its solution in an acetone/water mixture (70:30) in space group P61 with a=b=14.912(3) Å, c= 25.548(5) Å, V=4912.0(6) Å3. The structure was determined by direct methods and refined by a full matrix least-squares procedure to an R value of 0.079 for 2891 observed [I≥3σ(I)] reflections. The backbone torsion angles φ1=-54(1)°, ψ1= 129(1)°, ω1=-177(1)°, φ2 =57(1)°, ψ2=15(1)°, ω2 =-170(1)°, φ3=80(1)°, ψ3 =7(2)°, ω3=-177(1)°, φ4 =-108(1)° and ψT4=-34 (1)° suggest that the peptide adopts a folded conformation with two overlapping β-turns of types II and III′. These turns are stabilized by two intramolecular hydrogen bonds between the CO of the Boc group and the NH of ΔPhe3 and the CO of Val1 and the NH of Ala4. The torsion angles of ΔPhe2 and ΔPhe3 side chains are similar and indicate that the two ΔPhe residues are essentially planar. The folded molecules form head-to- tail intermolecular hydrogen bonds giving rise to continuous helical columns which run parallel to the c-axis. This structure established the formation of two β-turns of types II and III′ respectively for sequences containing two consecutive ΔPhe residues at (i+2) and (i+3) positions with a branched β-carbon residue at one end of the tetrapeptide.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/psc.77
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