ISSN:
0887-3585
Keywords:
hydrophobic α-helices
;
water insertion into helix
;
water in hydrophobic pocket
;
helix unfolding
;
helix folding
;
parallel packing
;
Chemistry
;
Biochemistry and Biotechnology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Medicine
Notes:
The crystal structures of two helical peptides Boc-Val-Ala-Leu-Aib-Val-Ala-Leu-OMe (VALU-7) and Boc-Val-Ala-Leu-Aib-Val-Ala-Leu-Aib-OMe (VALU-8) have been determined to a resolution of 1.0 and 0.9 Å, respectively. Both the seven and eight residue peptides crystallize with two conformers per asymmetric unit. The VALU-8 conformers are completely helical and differ only at the C-terminus by a sign reversal of the φ, ψ angles of the last residue. One of the VALUE-7 conformers occurs as a normal α-helix, whereas in the other, the N(7)=O(3) α-type hydrogen bond is ruptured by the entry of a water molecule (W) into the helix, which in turn makes hydrogen bonds N(7)⃛W = 2.97 Å and ⃛O(3) = 2.77 Å. The other side of the water molecule is surrounded by a hydrophobic pocket. These two conformers give a static representation of a step in a possible helix unwinding or folding process. In the value-8 crystal the helices aggregate in a parallel mode, whereas the aggregation is antiparallel in the VALU-7 crystal. The crystal parameters are VALUE-7 crystal. The crystal parameters are VALUE-7, P21, a = 10.203 (3) Å, b = 19.744 (6) Å, c = 22.561 (6) Å, α = 96.76°, Z = 4, C38, H69N7O10·0.5 H2O, R = 6.65% for 3674 reflections observed 〉3σ(F): and VALU-8, P21, a; = 10.596 (4) Å, b = 27.57 (6) Å, c = 17.745 (5) Å, β = 95.76 (3)°, Z = 4, C42H76N76O11·0.25 CH3OH, R = 6.63% for 4701 reflections observed 〉3σ(F).
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/prot.340070107
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