albumin - publications

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1. J Biomol Struct Dyn. 2012 Apr;29(5):1013-50.

Probing the interaction of human serum albumin with bilirubin in the presence of
aspirin by multi-spectroscopic, molecular modeling and zeta potential techniques:
insight on binary and ternary systems.

Hosainzadeh A, Gharanfoli M, Saberi MR, Chamani JK.

Department of Biology, Faculty of Sciences, Mashhad Branch, Islamic Azad
University, Mashhad, Iran. chamani@ibb.ut.ac.ir.

Here, we report on the effect of aspirin (ASA), on the binding parameters with
regard to bilirubin (BR) to human serum albumin (HSA). Two different classes of
binding sites were detected. Binding to the first and second classes of the
binding sites was dominated by hydrophobic forces in the case of HSA-BR, whereas
in the case of the ternary system, binding to the first and second classes of the
binding sites was achieved by electrostatic interaction. The binding constant
(K(a)) and number of binding site (n) obtained were 1.6 × 10(6)M(-1) and 0.98,
respectively, for the primary binding site in the case of HSA-BR, and 3.7 ×
10(6)M(-1) and 0.84, respectively, in the presence of ASA (ternary complex) at
λ(ex)= 280nm. The progressive quenching of the protein fluorescence as the BR
concentration increased indicated an arrangement of the domain IIA in HSA.
Changes in the environment of the aromatic residues were also observed by
synchronous fluorescence spectroscopy (SFS). Changes of the secondary structure
of HSA involving a decrease of α-helical and β-sheet contents and increased
amounts of turns and unordered conformations were mainly found at high
concentrations of BR. For the first time, the relationship between the structural
parameters of HSA-BR by RLS for determining the critical induced aggregation
concentration (C(CIAC)) of BR in the absence and presence of ASA was
investigated, and there was a more significant enhancement in the case of the
ternary mixture as opposed to the binary one. Changes in the zeta potential of
HSA and the HSA-ASA complex in the presence of BR demonstrated a hydrophobic
adsorption of this anionic ligand onto the surface of HSA in the binary system as
well as both electrostatic and hydrophobic adsorption in the case of the ternary
complex. By performing docking experiments, it was found that the acting forces
between BR and HSA were mainly hydrophobic > hydrogen bonding > electrostatic
interactions, and consequently BR had a long storage time in blood plasma,
especially in the presence of ASA. This was due to the electrostatic interaction
force between the BR and HSA being stronger in (HSA-ASA) BR than in the HSA-BR
complex. In addition, it was demonstrated that, in the presence of ASA, the first
binding site of BR on HSA was altered, but the parameters of binding did not
become significantly modified, and thus the affinity of BR barely changed with
and without ASA.

PMID: 22292958 [PubMed - in process]