Zinc induces disorder-to-order transitions in free and membrane-associated Thellungiella salsuginea dehydrins TsDHN-1 and TsDHN-2: a solution CD and solid-state ATR-FTIR study

Abstract

Dehydrins are intrinsically unstructured proteins that are expressed in plants experiencing extreme environmental conditions such as drought or low temperature. Although their role is not completely understood, it has been suggested that they stabilize proteins and membrane structures during environmental stress and also sequester metals such as zinc. Here, we investigate two dehydrins (denoted as TsDHN-1 and TsDHN-2) from Thellungiella salsuginea. This plant is a crucifer that thrives in the Canadian sub-Arctic (Yukon Territory) where it grows on saline-rich soils and experiences periods of both extreme cold and drought. We show using circular dichroism and attenuated total reflection-Fourier transform infrared spectroscopy that ordered secondary structure is induced and stabilized in these proteins, both in free and vesicle-bound form, by association with zinc. In membrane-associated form, both proteins have an increased proportion of β-strand conformation induced by the cation, in addition to the amphipathic α-helices formed by their constituent K-segments. These results support the hypothesis that dehydrins stabilize plant plasma and organellar membranes in conditions of stress, and further that zinc may be an important co-factor in stabilization. Whereas dehydrins in the cytosol of a plant cell undergoing dehydration or temperature stress form bulk hydrogels and remain primarily disordered, dehydrins with specific membrane- or protein-associations will have induced ordered secondary structures.

The K-segments of wheat dehydrin WZY2 are essential for its protective functions under temperature stress

“…Actinidia chinensis DHN1 is normally located in the nucleus and then moves to the cytoplasm near the plasma membrane in response to osmotic stress (Qiu et al, 2001). Based on available evidence, DHNs move toward the plasma membrane and intracellular membrane systems during cold acclimation, a result that is consistent with DHNs’ binding gain of membrane stability in vitro (Koag et al, 2003, 2009; Rahman et al, 2010, 2011a,b; Rahman, 2012). However, our results conflict with this notion.…”

Disorder and function: a review of the dehydrin protein family

“…Using synthetic peptides, Hara et al (2005) showed that there is no ion binding to the K-segments, and that the strongest binding is to the sequence HKGEHHSGDHH, likely due to the His-His dipeptides. A similar study was carried out by Rahman et al (2011) with TsDHN1 and TsDHN2 using isothermal calorimetry (ITC) to characterize metal binding. In the presence of Zn(II), it was shown that there were two zinc binding sites on TsDHN1 with a K d of 45 μM, while there was one zinc binding site on TsDHN2 with a K d of 26 μM.…”

Multifarious Roles of Intrinsic Disorder in Proteins Illustrate Its Broad Impact on Plant Biology

“…The functions of LEA proteins have been characterized mainly by in vitro experiments. These include binding of metal ions (Heyen et al, 2002;Hara et al, 2005;Rahman et al, 2011b) or lipid vesicles (Koag et al, 2003;Kovacs et al, 2008;Rahman et al, 2010), hydration or ion sequestration (McCubbin et al, 1985;Tompa et al, 2006), and, remarkably, stabilization of proteins and membranes in adaptation to abiotic stress ( Figure 2A, I to III). The latter function includes protection of various proteins against heat-induced inactivation or aggregation under stress conditions (Haaning et al, 2008;Boucher et al, 2010) and protection of membranes against drying and chilling (Tolleter et al, 2007;Rahman et al, 2010;Tolleter et al, 2010).…”

“…Different dehydrins have also been found to have multiple modes of ion binding: The acidic group 2b LEA dehydrins show phosphorylation-dependent metal-ion binding (Alsheikh et al, 2005), whereas Cu-COR15 (for Cold-Regulated) from Citrus unshiu shows metal-ion binding without phosphorylation (Hara et al, 2005). Some LEA proteins acquire secondary structure through bindinginduced folding upon binding to partners, metal ions, and model membranes (Koag et al, 2009;Rahman et al, 2010Rahman et al, , 2011b or upon drying (Boudet et al, 2006;Thalhammer et al, 2010;Popova et al, 2011), whereas for other dehydrins, neither temperature, metal ions, nor stabilizing agent promoted structural folding (Mouillon et al, 2006). It seems the role of the conserved segments within these nonfoldable dehydrins is to act as beads on a string for specific recognition or interaction with membranes rather than promoting tertiary structure formation.…”