LEA_4 motifs act synergistically with drying-enriched metabolites to increase their protective ability.

Abstract

Intrinsically disordered Family 4 Late Embryogenesis Abundant (LEA_4) proteins are important in many organisms’ ability to survive extreme drying, or desiccation. Interestingly, these proteins adopt novel structures upon desiccation, which is thought to confer their protective capabilities. Specifically, it is believed that conserved 11-residue motifs in LEA_4 proteins become more helical in water deficient environments, which enables them to protect sensitive proteins in the cell. However, this is not the only situation in which LEA_4 protein structure is altered. Like other IDPs, LEA_4 proteins are highly sensitive to their chemical environment, changes to which can lead them to adopt different structures. During desiccation, many organisms change their chemical environment by enriching metabolites. This can change the ensembles of LEA_4 motifs, which would potentially change or modify their function(s). One such modification could be a synergistic effect, in which desiccation-enriched metabolites alter the ensemble of LEA_4 motifs to increase their protective ability.Here we explore this possibility, examining the effect of desiccation-enriched metabolites on LEA_4 motifs’ ability to protect a protein during desiccation. LEA_4 motifs from a variety of different organisms were benchmarked by their ability to protect a desiccation sensitive enzyme, citrate synthase. When exposed to drying-enriched metabolites, these motifs show several-fold increases in their protective ability. We also explore possible mechanistic causes for this synergistic effect, such as alterations in the motifs’ ensemble or in the physiochemical properties of motifs after desiccation. These results represent the first observations of synergistic protection in LEA_4 motifs. Furthermore, they serve as an explanation for the enrichment of metabolites during desiccation that have little or no direct protective benefit. Ultimately, these finding represent progress towards understanding how organisms survive desiccation, which has been an enduring mystery in the stress tolerance field.