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

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• 作者：Shigenori Nagatomo ; Masako Nagai ; Takashi Ogura ; Teizo Kitagawa
• 刊名：The Journal of Physical Chemistry B
• 出版年：2013
• 出版时间：August 15, 2013
• 年：2013
• 卷：117
• 期：32
• 页码：9343-9353
• 全文大小：621K
• 年卷期：v.117,no.32(August 15, 2013)
• ISSN：1520-5207

文摘

Near-UV circular dichroism (CD) and UV resonance Raman (UVRR) spectra of l-tryptophan (Trp), its derivatives, and indole-C₃ 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鈥?90 nm, L_b transition) often with vibronic structures. All the indole-C₃ derivatives except for l-Trp gave no CD bands for L_a and L_b transitions, indicating that the asymmetric carbon (C_伪) connected through C₃鈥揅_尾 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-C₃ 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 蟽-bonds containing C_伪 and thus influence both chirality of L_a and L_b transitions and properties of the B_b excited state.