Albumin-bilirubin binding mechanism

Area of Science:

• Biochemistry
• Biophysics
• Physical Chemistry

Background:

• Bilirubin binding to human serum albumin (HSA) induces conformational changes.
• Understanding these dynamic processes is crucial for drug delivery and understanding physiological conditions.

Purpose of the Study:

• To investigate the late-stage conformational changes of HSA upon bilirubin binding.
• To explore the influence of fatty acid anions and pH on these conformational dynamics.
• To compare the binding and conformational effects of bilirubin versus xanthobilirubinate.

Main Methods:

• Spectroscopic analysis of light absorption changes over time (1-500s).
• Solvent perturbation spectroscopy using sucrose.
• Competitive binding studies using specific ligands to probe albumin binding sites.
• Comparative analysis of bilirubin and xanthobilirubinate binding to HSA.

Main Results:

• HSA exhibits late conformational changes after 1:1 bilirubin binding, observable via light absorption.
• Fatty acid anion binding and a pH jump (6 to 9) induce similar late conformational changes.
• Xanthobilirubinate, possessing a single chromophore, does not induce these late conformational changes upon binding to HSA.
• Solvent perturbation studies did not reveal significant exposure of bilirubin chromophores.

Conclusions:

• Late conformational changes in HSA-bilirubin complexes are likely due to the rotation of albumin half-domains affecting exciton splitting.
• The presence of two chromophores in bilirubin, compared to one in xanthobilirubinate, is essential for these observed late conformational dynamics.
• The findings support a model involving domain rotation and exciton splitting in HSA conformational changes.