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Direct evidence for alteration of unfolding profile of a helical peptide by far‐ultraviolet circular dichroism aromatic side‐chain contribution
Author(s) -
Banerjee Raja,
Basu Gautam
Publication year - 2002
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(02)02974-5
Subject(s) - side chain , circular dichroism , chemistry , peptide , crystallography , stereochemistry , alanine , transition (genetics) , helix (gastropod) , amino acid , organic chemistry , biochemistry , ecology , biology , snail , gene , polymer
Aromatic side‐chains are known to contribute to the far‐UV circular dichroism (CD) spectra of peptides and proteins. Among other things, this can significantly affect the measured helix propensities of amino acids [Chakrabartty et al., Biochemistry 32 (1993) 5560–5565]. In order to address how interfering side‐chain contributions can affect the backbone unfolding transition of a helical peptide, as monitored by [ θ ] 222 (molar ellipticity at 222 nm), we have studied the unfolding transition of a short designed (α‐amino isobutyric acid/alanine‐based) helical peptide containing an interacting Tyr residue. The guanidinium hydrochloride‐induced unfolding of the peptide, as monitored by [ θ ] 222 , showed the presence of a sharp transition superposed over a much broader transition. When the same experiment was performed with a similar peptide that lacked the interacting Tyr residue, the sharp transition disappeared and only the broad transition remained. The sharp transition was assigned to originate from the interacting Tyr side‐chain. This demonstrates that conformationally restricted aromatic side‐chains that interact with the helical backbone not only can alter the backbone far‐UV CD signal, they may also alter the unfolding profiles, monitored by far‐UV CD, rendering them unfit for a simple analysis for extracting the appropriate unfolding thermodynamic parameters.