The accumulation of Late Embryogenesis Abundant (LEA) proteins in plants is associated with tolerance against
stresses such as freezing and desiccation. Two main functions have been attributed to LEA proteins: membrane
stabilization and enzyme protection. We have hypothesized previously that LEA7 from Arabidopsis thaliana
may stabilize membranes because it interacts with liposomes in the dry state. Herewe show that LEA7, contrary
to this expectation, did not stabilize liposomes during drying and rehydration. Instead, it partially preserved the
activity of the enzyme lactate dehydrogenase (LDH) during drying and freezing. Fourier-transform infrared
(FTIR) spectroscopy showed no evidence of aggregation of LDH in the dry or rehydrated state under conditions
that lead to complete loss of activity. To approximate the complex influence of intracellular conditions on the protective
effects of a LEA protein in a convenient in-vitro assay, we measured the activity of two Arabidopsis enzymes
(glucose-6-P dehydrogenase and ADP-glucose pyrophosphorylase) in total soluble leaf protein extract
(Arabidopsis soluble proteome, ASP) after drying and rehydration or freezing and thawing. LEA7 partially preserved
the activity of both enzymes under these conditions, suggesting its role as an enzyme protectant
in vivo. Further FTIR analyses indicated the partial reversibility of protein aggregation in the dry ASP during rehydration.
Similarly, aggregation in the dry ASP was strongly reduced by LEA7. In addition, mixtures of LEA7
with sucrose or verbascose reduced aggregation more than the single additives, presumably through the effects
of the protein on the H-bonding network of the sugar glasses.
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