RESUMO
The infrared absorption and vibrational circular dichroism (VCD) spectra of buffered aqueous solutions of cytidylyl-(3'-5')-guanosine (5'(CG)3') and guanylyl-(3'-5')-cytidine (5'(GC)3') are reported. Under low ionic strength conditions, these dinucleotides exhibit VCD features that can be predicted qualitatively from structural data of (CG)2 and (GC)2 sequences of poly(dG-dC).poly(dG-dC), using the exciton model for infrared VCD intensities.
Assuntos
DNA/química , Fosfatos de Dinucleosídeos/química , Fenômenos Biofísicos , Biofísica , Dicroísmo Circular , Modelos Moleculares , Estrutura Molecular , Conformação de Ácido Nucleico , Polidesoxirribonucleotídeos/química , Soluções , Espectrofotometria InfravermelhoRESUMO
Infrared (vibrational) circular dichroism (VCD) spectra have been obtained for the self-complementary tetranucleotides, 5'd(CGCG)3', 5'd(GCGC)3', 5'd(CCGG)3', and 5'd(GGCC)3'. In buffered aqueous solution at low salt concentration, these tetramers exhibit spectra associated with right-handed polymers, although the spectra differ significantly for the four species. In high salt solution, a B-->Z transition occurs in 5'd(CGCG)3', while the other tetranucleotides appear only slightly altered. Temperature dependent studies of these oligonucleotides reveal a greater amount of thermal stability for the tetramers in low salt than for the high salt solutions. VCD intensities computed via the exciton formalism are compared with observed results.
Assuntos
Oligodesoxirribonucleotídeos/química , Sequência de Bases , Fenômenos Biofísicos , Biofísica , Dicroísmo Circular , Conformação de Ácido Nucleico , Desnaturação de Ácido Nucleico , Concentração Osmolar , Sais , Soluções , Espectrofotometria Infravermelho , Temperatura , Termodinâmica , ÁguaRESUMO
The infrared vibrational circular dichroism (VCD) spectral features of prototypical peptide secondary structures were reported previously by Yasui and Keiderling [Yasui, S.C., & Keiderling, T.A. (1986) Biopolymers 25, 5]. These results demonstrated that the "random coil" peptide conformation exhibits VCD signals which are approximately mirror-image features of those exhibited by alpha-helical conformers. We report here a comparison of observed VCD spectra with those computed for several secondary structures, using the extended coupled oscillator formalism employed previously to compute VCD spectra of model DNA [Zhong et al. (1990) Biochemistry 29, 7485]. These studies suggest that the so-called random-coil peptide conformation has distinct short-range order and appears to be a left-handed, helical structure.
