The effects of drug complexation on the stability and conformation of human serum albumin

Abstract

We report different analytical methods used to study the effects of 3′-azido-3′-deoxythymidine, aspirin, taxol, cisplatin, atrazine, 2,4-dichlorophenoxyacetic, biogenic, polyamines, chlorophyll, chlorophyllin, poly(ethylene glycol), vanadyl cation, vanadate anion, cobalt-hexamine cation, and As₂O₃, on the stability and secondary structure of human serum albumin (HSA) in aqueous solution, using capillary electrophoresis. Fourier transform infrared, ultraviolet visible, and circular dichroism (CD) spectroscopic methods. The concentrations of HSA used were 4% to 2% or 0.6 to 0.3 mM, while different ligand concentrations were 1μM to 1 mM. Structural data showed drugs are mostly located along the polypeptide chains with both specific and nonspecific interactions. The stability of drug-protein complexes were in the order K_VO ²⁺ 1.2×10⁸ M ⁻¹>K_AZT 1.9×10⁶ M ⁻¹>K_PEG 4.1×10⁵ M ⁻¹>K_atrazine 3.5×10⁴ M ⁻¹>K_chlorophyll 2.9×10⁴ M ⁻¹>K _2,4-D2.5×10⁴ M⁻¹>K_spermine 1.7×10⁴ M ⁻¹>K_taxol 1.43×10⁴ M ⁻¹>K_Co3+>1.1×10⁴ M ⁻¹>K_aspirin 1.04×10⁴i⁻¹>K_{chlorophyllin} 7.0×10³ M ⁻¹×K_VO3 ⁻6.0×10³ M ⁻¹>K_spermidine 5.4 ×10³ M ⁻¹>K_putrescine 3.9×10³ M ⁻¹>K_As2O₃, 2.2×10³ M ⁻¹>K_cisplatin 1.2×10² M ⁻¹. The protein conformation was altered (infrared and CD results) with major reduction of α-helix from 60 to 55% (free HSA) to 40 to 40% and increase of β-structure from 22 to 15% (free HSA) to 33 to 23% in the drug-protein complexes. The alterations of protein secondary, structure are attributed to partial, unfolding of HSA on drug complexation.