ABSTRACT
Dehydrins are well associated with the abiotic stress tolerance of the plants, such as dehydration, salt stress and cold stress. They include a highly conserved lysine-rich motif called K-segment, which is believed to play a significant role in dehydrin function. The K-segment shows in vitro antibacterial activity against Gram-positive bacteria like its full-length dehydrin protein. In this study, the structures of the K-segment from rice dehydrin have been investigated by CD spectroscopy, NMR and molecular dynamic simulation. The results reveal that the K-segment is disordered in aqueous solution, but adopts helical structure in mimetic membrane environment, sodium dodecyl sulfate (SDS) micelles. The central region of K-segment forms an a-helix and exhibits amphipathic arrangement,where hydrophobic residues locate on one side and hydrophilic residues are on the other side. The amphipathic feature allows the helix region of the K-segment to insert into the SDS micelles, resulting in stable association with mimetic membrane. To realize the energy minimization,the hydrophobic side of the helix faces to the hydrophobic core of SDS micelles,and the hydrophilic side of the helix faces to the surface of micelles. The precise 3D structure and orientation information of the K-segment obtained in this work might provide new insights in understanding the structure-function relationship of dehydrins.
ABSTRACT
The SH4 domain of Src family of nonreceptor protein tyrosine kinases represents the extreme N-terminal 1–16 amino acid region which mediates membrane association of these proteins and facilitates their functions. The SH4 domains among Src members lack well-defined sequence consensus and vary in the net charge. However, they readily anchor to the cytoplasmic face of the plasma membrane upon fatty acid acylation. Here, we report the membrane association of differentially acylated SH4 domain of Lck kinase, which has net negative charge at physiological pH. Our results suggest that despite the net negative charge, the SH4 domain of Lck associates with membranes upon fatty acid acylation. While myristoylation at the N-terminus is sufficient for providing membrane anchorage, multiple acylation determines orientation of the peptide chain with respect to the lipid bilayer. Hence, fatty acylation serves more than just a lipid anchor. It has an important role in regulating the spatial orientation of the peptide domain with respect to the lipid bilayer, which could be important for the interaction of the other domains of these kinases with their partners.