Apolar peptide models for conformational heterogeneity, hydration, and packing of polypeptide helices: Crystal structure of hepta‐ and octapeptides containing α‐aminoisobutyric acid
作者:
Isabella L. Karle,
Judith L. Flippen‐Anderson,
K. Uma,
P. Balaram,
期刊:
Proteins: Structure, Function, and Bioinformatics
(WILEY Available online 1990)
卷期:
Volume 7,
issue 1
页码: 62-73
ISSN:0887-3585
年代: 1990
DOI:10.1002/prot.340070107
出版商: Wiley Subscription Services, Inc., A Wiley Company
关键词: hydrophobic α‐helices;water insertion into helix;water in hydrophobic pocket;helix unfolding;helix folding;parallel packing
数据来源: WILEY
摘要:
AbstractThe 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 = 95.7
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