Ultrafast Spectroscopic Dynamics of Quinacrine-Riboflavin Binding Protein Interactions

Shiori Yamazaki, Matthew A. Diaz, Thomas M. Carlino, Chitra Gotluru, Mercedes M.A. Mazza, Amy M Scott

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


Redox active cofactors play a dynamic role inside protein binding active sites because the amino acids responsible for binding participate in electron transfer (ET) reactions. Here, we use femtosecond transient absorption (FsTA) spectroscopy to examine the ultrafast ET between quinacrine (Qc), an antimalarial drug with potential anticancer activity, and riboflavin binding protein (RfBP) with a known Kd = 264 nM. Steady-state absorption reveals a ∼ 10 nm red-shift in the ground state when QcH3 2+ is titrated with RfBP, and a Stern-Volmer analysis shows ∼84% quenching and a blue-shift of the QcH3 2+ photoluminescence to form a 1:1 binding ratio of the QcH3 2+-RfBP complex. Upon selective photoexcitation of QcH3 2+ in the QcH3 2+-RfBP complex, we observe charge separation in 7 ps to form 1[QcH3-red •+-RfBP•+], which persists for 138 ps. The FsTA spectra show the spectroscopic identification of QcH3-red +, determined from spectroelectrochemical measurements in DMSO. We correlate our results to literature and report lifetimes that are 10-20× slower than the natural riboflavin, Rf-RfBP, complex and are oxygen independent. Driving force (ΔG) calculations, corrected for estimated dielectric constants for protein hydrophobic pockets, and Marcus theory depict a favorable one-electron ET process between QcH3 2+ and nearby redox active tyrosine (Tyr) or tryptophan (Trp) residues.

Original languageEnglish (US)
Pages (from-to)8291-8299
Number of pages9
JournalJournal of Physical Chemistry B
Issue number35
StatePublished - Sep 7 2017

ASJC Scopus subject areas

  • Surfaces, Coatings and Films
  • Physical and Theoretical Chemistry
  • Materials Chemistry

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