Near-UV Circular Dichroism and UV Resonance Raman Spectra of Tryptophan Residues as a Structural Marker of Proteins

作者：Nagatomo Shigenori^*; Nagai Masako; Ogura Takashi; Kitagawa Teizo

来源：Journal of Physical Chemistry B, 2013, 117(32): 9343-9353.

DOI：10.1021/jp404685x

Near-UV circular dichroism (CD) and UV resonance Raman (UVRR) spectra of l-tryptophan (Trp), its derivatives, and indole-C-3 derivatives were investigated to utilize Trp signals of proteins as a structural marker. CD spectra of Trp are classified into four types: Free L-Trp gives type II (around 270 nm, L-a transition), while L-Trp in proteins generally yields type I (around 280-290 nm, L-b transition) often with vibronic structures. All the indole-C-3 derivatives except for L-Trp gave no CD bands for L-a and L-b transitions, indicating that the asymmetric carbon (C-alpha) connected through C-3-C-beta is essential to appearance of CD. We demonstrate here that the type of CD spectra is determined by a condition of the amino group of Trp; it was changed from type II to type I by the modification of the amino group. In contrast, the modification of the carboxyl group of L-Trp had little effects on a CD spectrum. The 229 nm excited UVRR spectra were almost the same between L-Trp and indole-C-3 derivatives. Comparison of CD and UVRR spectra of Trp residues in proteins suggested that mainly the W17 (possibly together with W16) mode contributes to the characteristic vibronic coupling of L-b transition. Both UVRR and CD spectra of L-Trp were influenced by protonation of amino and/or carboxyl groups, but those changes were distinguished from hydrogen bonding effects at N1H of indole. It is likely that these protonations are communicated to indole through sigma-bonds containing C-alpha and thus influence both chirality of L-a and L-b transitions and properties of the B-b excited state.

• 出版日期2013-8-15