Structural Transitions of Dehydrin in Response to Temperature, the Presence of Trifluoroethanol and Sodium Dodecyl Sulfate, and Its Protective Role in Heat and Cold Stress

The plant protein dehydrin of the late embryogenesis abundant (LEA) family plays an important role in abiotic stress tolerance. Here, we investigated the structural changes in DHN1 (dehydrin) protein from Zea mays (167 aa) upon exposure to varying temperatures and various concentrations of sodium dodecyl sulfate and trifluoroethanol, using spectroscopic techniques such as CD, fluorescence, and FRET. For this purpose, three mutants DHN1 CW1 (Cys⁶²─Trp¹²²), DHN1 CW2 (Cys⁶²─Trp¹³²), and DHN1 W3 (Trp³) were generated by replacing amino acids at sites between the two K-segments, near the S-segment and at the N-terminal. CD data revealed that DHN1 and its mutants CW1 and CW2 show substantial disorder to order (increased alpha helical content) transition on increasing temperature from 25 to 90 °C in contrast to the DHN1 W3 mutant. A large blue shift in tryptophan emission maxima, accompanied by rising Trp fluorescence anisotropy, increase in helical content accompanied by a reduction in the random coil structure of DHN1 revealed a transition from a disordered to ordered conformation in the presence of ∼0.2 mM SDS. Furthermore, intramolecular FRET between the Trp and Cys conjugated dansyl probe indicated that the distance between Trp¹²² and Cys⁶² in DHN1 CW1 was reduced from 34 to 26 Å in the presence of ∼0.4 mM SDS, while the distance between Trp¹³² and Cys⁶² in DHN1 CW2 was reduced from 24 to 22 Å. The DHN1 mutants displayed reduced cryoprotection but robust heat protection activity, with altered sensitivity to heat/SDS. Our results yield quantitative insights on the role of the N-terminal and K-segment, facilitating the folding of DHN1 triggered by exposure to anionic monomers of SDS.