Protein Unfolding in Drug-RNase Complexes

Abstract

Bovine pancreatic ribonuclease A (RNase A) catalyzes the cleavage of P-O5′ bonds in RNA on the 3′ side of pyrimidine to form cyclic 2′, 5′-phosphates. It has several high affinity binding sites that make it possible target for many organic and inorganic molecules. Ligand binding to RNase A can alter protein secondary structure and its catalytic activity. In this review, the effects of several drugs such as AZT (anti-AIDS), cis-Pt (antitumor), aspirin (anti-inflammatory), and vitamin C (antioxidant) on the stability and conformation of RNase A in vitro are compared. The results of UV-visible, FTIR, and CD spectroscopic analysis of RNase complexes with aspirin, AZT, cis-Pt, and vitamin C at physiological conditions are discussed here.

Spectroscopic results showed one major binding for each drug-RNase adduct with KAZT = 5.29 (±1.6) × 10⁴ M⁻¹, K_aspirin = 3.57 (±1.4) × 10⁴ M⁻¹, K_cis-pt = 5.66 (±1.9) × 10³ M⁻¹, and K_ascorbate = 3.50 (±1.5) × 10³ M⁻¹. Major protein unfolding occurred with reduction of α-helix from 29% (free protein) to 20% and increase of β-sheet from 39% (free protein) to 45% in the aspirin-, ascorbate-, and cis-Pt-RNase complexes, while minor increase of α-helix was observed for AZT-RNase adduct.

Key words:

• Protein
• Drug
• RNase A
• Binding mode
• Binding constant
• Secondary structure
• FTIR
• UV-Visible
• CD spectroscopy