Effects of betaine on the structural dynamics of Thermomyces ( Humicola) lanuginosa lipase

• Published in: Colloids and surfaces, B, Biointerfaces B, Biointerfaces, 2002-09, Vol.26 (1), p.75-83
• Main Authors: Söderlund, Tim, Zhu, Keng, Jutila, Arimatti, Kinnunen, Paavo K.J
• Format: Article
• Language: English
• Subjects: Differential scanning calorimetry; Hydration; Protein; Surface tension; Time-resolved fluorescence spectroscopy
• ISSN: 0927-7765; 1873-4367
• DOI: 10.1016/S0927-7765(02)00032-2

The impact of betaine on the structural dynamics of a soluble protein, Thermomyces ( Humicola) lanuginosa lipase (HLL) was studied using differential scanning calorimetry (DSC), surface tension measurements, and both steady-state and time-resolved fluorescence spectroscopy. Betaine increased the thermal stability of wild type HLL and protected this enzyme from unfolding by the chaotrope, guanidine hydrochloride. Time-resolved fluorescence anisotropy measurements revealed betaine to decrease the mean hydrodynamic volume of the single Trp HLL mutant, W89m, and to reduce the movements of the α-helical segment constituting the so-called ‘lid’. In the presence of betaine, the average environment of Trp89 became more hydrophobic with decreased accessibility to this residue for the water soluble quencher I −, the bimolecular collisional rate constant, k q decreasing from 6.86×10 8 to 5.06×10 8 M −1 s −1 in 1.0 M betaine. The above results are in keeping with an augmented packing of the lipase in the presence of betaine. Betaine increases surface tension ( γ) of water and enhances the denaturation of HLL into the air–water interface. The increased stability of HLL and increased γ by betaine suggest low or no binding of betaine to the surface of protein. The effects of betaine on the structural dynamics of HLL are readily explained by the increased surface tension of water caused by this solute.