Flexibility of Na,K-ATPase Secondary Structure upon Drug-Protein Interaction

The enzyme Na+, K+-ATPase is an integral membrane protein which transports sodium and potassium cations against an electrochemical gradient. The transport of Na+ and K+ ions is connected to an oscillation of the enzyme between the two conformational states, the E1 (Na+) and the E2 (K+) conformations. The enzymatic activity of ATPase is largley affected by different ligands complexation. This review reports the effects of several drugs such as AZT (anti-AIDS), cis-Pt (antitumor), aspirin (anti-inflammatory) and vitamin C (antioxidant) on the stability and secondary structure of Na,K-ATPase in vitro. Drugenzyme binding is mainly through H-bonding to the polypeptide C=O and C-N groups with two binding constants K1(AZT) = 5.30 × 105 M-1 and K2(AZT) = 9.80 × 103 M-1 for AZT and one binding constant for Kcis-Pt = 1.93 × 104 M-1, Kaspirin = 6.45 × 103 M-1 and Kascorbate = 1.04 × 104 M-1 for cis-Pt, aspirin and ascorbic acid. The enzyme secondary structure was altered from that of a-helix 19.8% (free protein) to almost 22-26% and the b-sheet from 25.6% to 18-22%, upon drug complexation with the order of induced stability AZT > cis-Pt > ascorbate > aspirin