Abstract

Cationic, anionic, zwitterionic, and nonionic detergents differentially affect thermostability of pepper leaf proteins

Author(s): Dafang Wang, Jeff A.Anderson

Protein thermal stability is central to plant temperature stress responses as well as many practical enzyme applications. Considerable information has been acquired on interactions between specific pair-wise combinations of a protein and cosolute. However, little is known about interactions between complex protein mixtures, such as those found in plant cells, and cosolutes of various structural properties. Therefore, our objective was to determine the effects of four classes of detergents on solubility-based thermostability of pepper (Capsicum annuum L.) leaf proteins. The cationic detergent cetyltrimethylammoniumbromide (CTAB) decreased protein thermostabilitywith increasingCTAB concentration up to the concentration corresponding to the transition from CTAB monomers to micelles. However, higher concentrations of CTAB prevented turbidity and precipitation up to 100 °C. The anionic detergent sodium dodecyl sulfate (SDS) reduced pepper protein thermostability at lowconcentrations, butmaintained solubility at higher concentrations. Unlike CTAB, the transition fromdestabilization to stabilization occurred over a lower SDS concentration range than the transition from monomers to micelles. In contrast with CTAB and SDS, the nonionic detergent polyoxyethylenesorbitanmonolaurate (Tween 20) and the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate hydrate (CHAPS) only destabilized pepper leaf proteins at elevated temperatures, approachingmaxima at concentrations near the criticalmicellar concentrations. Results from this study support the hypothesis that destabilization results primarily from changes in hydrophobic interactions and stabilization occurs from charge repulsion limiting aggregation.