Cao Y, Qin Y, Bruist M, Gao S, Wang B, Wang H, Guo X. Formation and Dissociation of the Interstrand i-Motif by the Sequences d(XnC 4Y m) Monitored with Electrospray Ionization Mass Spectrometry.
JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2015;
26:994-1003. [PMID:
25862186 DOI:
10.1007/s13361-015-1093-2]
[Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Revised: 02/05/2015] [Accepted: 02/06/2015] [Indexed: 06/04/2023]
Abstract
Formation and dissociation of the interstrand i-motifs by DNA with the sequence d(X(n)C(4)Y(m)) (X and Y represent thymine, adenine, or guanine, and n, m range from 0 to 2) are studied with electrospray ionization mass spectrometry (ESI-MS), circular dichroism (CD), and UV spectrophotometry. The ion complexes detected in the gas phase and the melting temperatures (Tm) obtained in solution show that a non-C base residue located at 5' end favors formation of the four-stranded structures, with T > A > G for imparting stability. Comparatively, no rule is found when a non-C base is located at the 3' end. Detection of penta- and hexa-stranded ions indicates the formation of i-motifs with more than four strands. In addition, the i-motifs seen in our mass spectra are accompanied by single-, double-, and triple-stranded ions, and the trimeric ions were always less abundant during annealing and heat-induced dissociation process of the DNA strands in solution (pH = 4.5). This provides a direct evidence of a strand-by-strand formation and dissociation pathway of the interstrand i-motif and formation of the triple strands is the rate-limiting step. In contrast, the trimeric ions are abundant when the tetramolecular ions are subjected to collision-induced dissociation (CID) in the gas phase, suggesting different dissociation behaviors of the interstrand i-motif in the gas phase and in solution. Furthermore, hysteretic UV absorption melting and cooling curves reveal an irreversible dissociation and association kinetic process of the interstrand i-motif in solution.
Collapse