Deactivation and unfolding are uncoupled in a bacterial lipase exposed to heat, low pH and organic solvents

The lipase from Burkholderia glumae (BGL) was incubated at variable temperature, pH and concentration of organic solvents, and the decrease of enzymatic activity was compared to changes in the molecular structure as monitored by ESI-mass spectrometry. We observed that deactivation is not strictly related to structural instability in the assay conditions, in fact (i) thermal deactivation preceded denaturation; (ii) acid-induced deactivation arose at higher pH than partial or global protein unfolding; and (iii) activity in most organic solvents decreased at solvent concentrations where conformation was fully retained. In particular, no denaturation at all could be elicited by dimethyl formamide (DMF), isopropanol, and dimethyl sulfoxide (DMSO) up to 80%, in spite of a reduction of enzyme activity to 60–75%.