Alpha-helical structure in the C-terminus of vasoactive intestinal peptide: functional and structural consequences.
The conformational properties of vasoactive intestinal peptide (VIP) include the N-terminal randomized structure and the C-terminal long alpha-helical structure. We have previously observed that the N-terminal random coil structure plays a crucial role in the receptor-selectivity. Here, to clarify how the formation of the alpha-helix plays a role in its biological functions, we chemically synthesized VIP analogues modified at the C-terminus, mid-chain, and N-terminus of the alpha-helical region, and evaluated the relationship between their alpha-helical contents and their biological activities including relaxant effects on murine stomach and receptor-binding activities. VIP and VIP-(1-27) showed equipotent biological activities with 48% and 50% alpha-helical content, respectively, each of which corresponds to 14 amino acid residues. VIP-(1-26) was 10% and threefold less potent in relaxant and binding activities, respectively, compared with VIP, and its 49% alpha-helical content resulted in 13 residues involved in the alpha-helix. Further truncation from 25 to 21 resulted in decrease in the alpha-helical content from 43% to 29%, corresponding residues from 11 to 6, the relaxant activity from 72% to 4%, and the affinity to the membrane from 60-fold to over 10(4)-fold less potency. In addition, disruption of the mid-chain and the N-terminus in the alpha-helical stretch by oxidation of Met(17) and deletion of Thr(11) also inhibited biological activities. These findings suggest that the presence of alpha-helical structure forming in 14 amino acid residues between position 10 and 23 in VIP is essential to its biological functions and the C-terminal amino acid residues between position 24 and 27 are requisite for this alpha-helical formation.
Onoue
Satomi
S
Health Science Division, Itoham Foods Inc., 1-2-1 Kubogaoka, Moriya, Ibaraki 302-0104, Japan. onoue@fureai.or.jp
Matsumoto
Asami
A
Nagano
Yumiko
Y
Ohshima
Keiichi
K
Ohmori
Yuki
Y
Yamada
Shizuo
S
Kimura
Ryohei
R
Yajima
Takehiko
T
Kashimoto
Kazuhisa
K
D000595:Amino Acid Sequence; D000818:Animals; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D008969:Molecular Sequence Data; D009119:Muscle Contraction / Q000502:physiology; D010446:Peptide Fragments / Q000737:chemistry* / Q000502:physiology*; D011485:Protein Binding; D017433:Protein Structure, Secondary / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013270:Stomach / Q000502:physiology; D013329:Structure-Activity Relationship; D014660:Vasoactive Intestinal Peptide / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology
D010446:Peptide Fragments; D014660:Vasoactive Intestinal Peptide