Ionic strength-dependent denaturation of Thermomyces lanuginosus lipase induced by SDS

▸ Thermomyces lanuginosus lipase (TlL) is denatured by SDS at low ionic strength. ▸ The SDS-denatured state contains secondary but no native, tertiary structure. ▸ TlL is not denatured by SDS at high ionic strength. ▸ Denaturation is correlated with the effect of ionic strength on micelle formation. Triglyceride lipase from Thermomyces lanuginosus (TlL) has been reported to be resistant to denaturation by sodium dodecyl sulfate (SDS). We have found that at neutral pH, structural integrity is strongly dependent on ionic strength. In 10mM phosphate buffer and SDS, the lipase exhibits a far-UV CD spectrum similar to other proteins denatured in this surfactant while the near-UV CD spectrum shows a complete loss of tertiary structure, observations supported by steady state fluorescence spectroscopy. However, when increasing the ionic strength by the addition of NaCl, the lipase was rendered resistant towards SDS denaturation, as observed by all techniques employed. The effect of salt on the critical micelle concentration (CMC) of SDS was observed to correlate with the effect on the degree of SDS-induced denaturation. This finding is compatible with the notion that the concentration of SDS monomers is a crucial factor for SDS–lipase interactions. The presented results are important for the understanding and improvement of protein stability in surfactant systems.