Characterization of two soybean (Glycine max L.) LEA IV proteins by circular dichroism and Fourier transform infrared spectrometry.

Late embryogenesis-abundant (LEA) proteins, accumulating to a high level during the late stages of seed development, may play a role as osmoprotectants. However, the functions and mechanisms of LEA proteins remained to be elucidated. Five major groups of LEA proteins have been described. In the present study, we report on the characterization of two members of soybean LEA IV proteins, basic GmPM1 and acidic GmPM28, by circular dichroism and Fourier transform infrared spectroscopy. The spectra of both proteins revealed limited defined secondary structures in the fully hydrated state. Thus, the soybean LEA IV proteins are members of 'natively unfolded proteins'. GmPM1 or GmPM28 proteins showed a conformational change under hydrophobic or dry conditions. After fast or slow drying, the two proteins showed slightly increased proportions of defined secondary structures (alpha-helix and beta-sheet), from 30 to 49% and from 34 to 42% for GmPM1 and GmPm28, respectively. In the dehydrated state, GmPM1 and GmPM28 interact with non-reducing sugars to improve the transition temperature of cellular glass, with poly-l-lysine to prevent dehydration-induced aggregation and with phospholipids to maintain the liquid crystal phase over a wide temperature range. Our work suggests that soybean LEA IV proteins are functional in the dry state. They are one of the important components in cellular glasses and may stabilize desiccation-sensitive proteins and plasma membranes during dehydration.

Gene cloning and characterization of a soybean (Glycine max L.) LEA protein, GmPM16.

Late embryogenesis abundant (LEA) proteins, present in abundance in seeds during the late stages of development, are associated with desiccation tolerance. In the present work, we characterize a soybean LEA protein, GmPM16, with low molecular weight, high pI value, and an unusual amino acid residue distribution along the protein. The transcripts were detected in cotyledon mesophyll cells but not in the vascular system of mature or pod-dried soybean seeds. Circular dichroism (CD) analysis and Fourier transfer infrared (FTIR) spectroscopy indicated that the GmPM16 protein in solution was highly unordered, possessing only partial alpha-helical structures. However, the protein in sodium dodecyl sulfate (SDS) or trifluoroethanol (TFE) solution or in a dry state exhibited a conformation of abundant alpha-helical structures. As well, the GmPM16 protein interacts with sugar and forms tightly glassy matrixes in the dry state. The protein may play a role in reducing cellular damage in drying seeds by changing the protein conformation and forming tight cellular glasses.