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Comparison of α‐helix stability in peptides having a negatively or positively charged residue block attached either to the N‐ or C‐terminus of an α‐helix: The electrostatic contribution and anisotropic stability of the α‐helix
Author(s) -
Takahashi Sho,
Kim EuiHo,
Hibino Takeshi,
Ooi Tatsuo
Publication year - 1989
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360280507
Subject(s) - helix (gastropod) , chemistry , random coil , alpha helix , electrostatics , dipole , crystallography , electromagnetic coil , anisotropy , circular dichroism , physics , organic chemistry , quantum mechanics , ecology , snail , biology
An estimation of the thermodynamic effects of a charged random coil, which is attached either to the N‐ or C‐terminus of polyalanine, upon α‐helix stability is attempted. A temperature‐induced helix‐coil transition of Ala 20 Lys 20 Phe and Lys 20 Ala 20 Phe was studied under various conditions of salt concentration and pH. By combining the results with previous ones for Ala 20 Glu 20 Phe and Glu 20 Ala 20 Phe, which have opposite electric charges to the present system [S. Ihara et al. (1982) Biopolymers 21 , 131–145], the free energy of the coil to helix transition of the polyalanine block could be separated into two terms—one term for the electrostatic interaction of electric charges in the random‐coil block with the α‐helix dipole, and a second term for the intrinsic stability of the helix. The first term indicates the significance of the helix dipole‐charge interactions, which affects the helix stability depending on the attaching side of the charged block and on the sign of the charges. This clearly shows the anisotropic stability of the α‐helix. Furthermore, analysis of the dependence of these thermodynamic quantities on salt concentrations showed, assuming that the effect of the attached electric charges was symmetric (in other words, the absolute values of the electrostatic interaction terms were independent of the sign of electric charges), that the intrinsic stability of the α‐helix was dependent on which side of the helix was attached to the random coil: a random coil attached to the N‐terminus of the α‐helix had little effect while that attached to a C‐terminal significantly destabilized the helix.