The binding of maize dehydrin1 to anionic phospholipid vesicles and the role of K-segment in the lipid binding

Dehydrins (late embryogenesis abundant (LEA) D-11, DHNs) are a family of plant proteins induced in response to abiotic stresses such as drought, low temperature, and salinity or during the late stages of embroygenesis. DHNs are typified by combinations of sequence motifs referred to as the K-segment, Y-segment, S-segment, and &phis;-segment. DHNs also have distinctive biophysical properties including high hydrophilicity, and solubility at high temperatures. They are intrinsically unstructured. On the basis of their unusual compositional and biophysical properties and because of their typical induction in response to abiotic stress, several hypothetical functions of DHNs have been proposed. DHNs contain at least one copy of a consensus fifteen amino acid sequence, the "K-segment". It is speculated that the K-segment forms a class A2 amphipathic alpha-helical, lipid-binding domain. The purpose of this work is to study whether DHNs bind lipids, bilayers, or phospholipid vesicles and what the role of the K-segment is in the lipid binding activity of DHNs.;It is shown that maize (Zea mays) dehydrin1 (DHN1) can bind to lipid vesicles that contain acidic phospholipids. It is also observed that DHN1 bind more favorably to vesicles of smaller diameter than to larger vesicles and that the association of DHN1 with vesicles results in an apparent increase of alpha-helicity of the proteins.;To identify the role of the K-segment of DHNs in vesicle binding, three K-segment(s) deletion proteins of maize DHN1 were produced using site directed mutagenesis. The in vitro lipid vesicle binding assays performed with these deletion proteins reveals that the K-segment is required for binding to anionic phospholipid vesicles. In addition, it is found that adoption of alpha-helicity of the K-segment accounts for the overall conformational change of DHNs upon binding to anionic phospholipid vesicles.;To understand further the structural properties of DHNs, DHNs1 in solution has been examined using multi-dimensional heteronuclear NMR spectroscopy. DHN1 bound to SDS and K-segment(s) deletion proteins of DHN1 have also been studied to characterize the interaction between DHN1 and lipid vesicles. DHN1 is unfolded and very flexible at physiological pH and the K-segment is involved in the binding to SDS.;In conclusion, DHNs seem to undergo function-related structural changes at the water/membrane interface, which may contribute to the stabilization of vesicles or other endomembrane structures under stress conditions.