Ali Mohd Sajid, Amina Musarat, Al-Lohedan Hamad A, Al Musayeib Nawal M
Department of Chemistry, College of Science, King Saud University, P.O. Box 2455, Riyadh, 11451, Arriyadh, Saudi Arabia.
Department of Pharmacognosy, College of Pharmacy, King Saud University, P.O. Box 2457, Riyadh, 11451, Arriyadh, Saudi Arabia.
Luminescence. 2017 Mar;32(2):223-230. doi: 10.1002/bio.3172. Epub 2016 Jun 15.
A sipholane triterpenoid, named sipholenone A, with anti-cancer properties was isolated from the Red Sea sponge Siphonochalina siphonella and characterized by proton and carbon-13 nuclear magnetic resonance ( H NMR and C NMR) spectroscopies. The goal of this study was to visualize the binding of this triterpenoid with human serum albumin (HSA) and to determine its binding site on the biomacromolecule. The interaction was visualized using fluorescence quenching, synchronous fluorescence, far- and near-UV circular dichroism (CD), UV-visible and Fourier transform-infrared (FT-IR) spectroscopies. UV-visible spectroscopy indicated the formation of a ground-state complex as a result of the interaction. Sipholenone A quenches the fluorescence of HSA via a static quenching mechanism. A small blue shift in the fluorescence quenching profiles suggested the involvement of hydrophobic forces in the interaction. Sipholenone A binding takes place at site I of subdomain II A with a 1:1 binding ratio, as revealed by displacement binding studies using warfarin, ibuprofen and digitoxin. Far-UV CD and FT-IR studies showed that the binding of sipholenone A to HSA also had a small effect on the protein's secondary structure with a slight decrease in the α-helical content. Several thermodynamic parameters were calculated, along with Forster's radiative energy transfer analysis.
