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Apolar peptide models for conformational heterogeneity, hydration, and packing of polypeptide helices: Crystal structure of hepta‐ and octapeptides containing α‐aminoisobutyric acid
Author(s) -
Karle Isabella L.,
FlippenAnderson Judith L.,
Uma K.,
Balaram P.
Publication year - 1990
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.340070107
Subject(s) - conformational isomerism , crystallography , hydrogen bond , chemistry , antiparallel (mathematics) , crystal structure , molecule , helix (gastropod) , stereochemistry , crystal (programming language) , physics , ecology , organic chemistry , quantum mechanics , snail , magnetic field , biology , computer science , programming language
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, P 2 1 , a = 10.203 (3) Å, b = 19.744 (6) Å, c = 22.561 (6) Å, α = 96.76°, Z = 4, C 38 , H 69 N 7 O 10 ·0.5 H 2 O, R = 6.65% for 3674 reflections observed >3σ(F): and VALU‐8, P 2 1 , a ; = 10.596 (4) Å, b = 27.57 (6) Å, c = 17.745 (5) Å, β = 95.76 (3)°, Z = 4, C 42 H 76 N 76 O 11 ·0.25 CH 3 OH, R = 6.63% for 4701 reflections observed >3σ(F).