Abstract
Biosurfactants (BS) are surface-active molecules produced by microorganisms. Their combination of useful properties and sustainable production make them promising industrial alternatives to petrochemical and oleochemical surfactants. Here we compare the impact of the anionic BS rhamnolipid (RL) and the conventional/synthetic anionic surfactant sodium dodecyl sulfate (SDS) on the structure and stability of three different commercially used enzymes, namely the cellulase Carezyme® (CZ), the phospholipase Lecitase Ultra® (LT) and the α-amylase Stainzyme® (SZ). Our data reveal a fundamental difference in their mode of interaction. SDS shows great diversity of interaction toward the different enzymes. It efficiently unfolds both LT and CZ, but LT is unfolded by SDS through formation of SDS clusters on the enzyme well below the cmc, while CZ is only unfolded by bulk micelles and on average binds significantly less SDS than LT. SDS binds with even lower stoichiometry to SZ and leads to an increase in thermal stability. In contrast, RL does not affect the tertiary or secondary structure of any enzyme at room temperature, has little impact on thermal stability and only binds detectably (but at low stoichiometries) to SZ. Furthermore, all enzymes maintain activity at both monomeric and micellar concentrations of RL. We conclude that RL, despite its anionic charge, is a surfactant that does not compromise the structural integrity of industrially relevant enzymes. This makes RL a promising alternative to current synthetic anionic surfactants in a wide range of commercial applications.
Highlights
Washing detergents are complex formulations that among many other components include surfactants and enzymes
Materials Tris was from AppliChem (Darmstadt, Germany), and sodium dodecyl sulfate (SDS), 4-nitrophenyl-α-D-maltohexaoside and 4nitrophenyl butyrate was from Sigma-Aldrich
We undertook this study to compare the impact of the synthetic surfactant SDS and the microbially produced biosurfactant RL on the structure, stability and enzymatic activity of 3 widely used industrial enzymes
Summary
Washing detergents are complex formulations that among many other components include surfactants and enzymes. Both surfactants and enzymes have key roles in the cleaning process. Surfactants are surface active agents that serve several roles, including reduction of surface tension, solubilization of stains and preventing redeposit. Enzymes catalyze the breakdown of difficult stains but can act directly on fabric. The addition of enzymes to detergent formulation has made it possible to reduce washing temperatures dramatically and thereby reduce energy costs. During washing processes (and during storage in liquid detergent formulations), surfactants
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