Hydrophilins from distant organisms can protect enzymatic activities from water limitation effects in vitro

Hydrophilins are a wide group of proteins whose defining characteristics are high hydrophilicity index (> 1.0) and high glycine content (> 6%). The transcripts of most hydrophilins accumulate in response to water deficit in organisms such as plants, fungi and bacteria. In plants, most of the known Late Embryogenesis Abundant (LEA) proteins belong to this group (Garay-Arroyo et al., Journal of Biological Chemistry 275, 5668–5674, 2000). To gain insight into the function of hydrophilins, an in vitro assay was developed in which the enzymes malate dehydrogenase (MDH) or lactate dehydrogenase (LDH) are subjected to controlled partial water removal. Subtle changes in conformation during partial water removal were detected using 1anilinonaphtalene-8-sulphonate (ANS), a fluorescent probe, whose emission at 460 nm increases when bound to hydrophobic groups. The results show that water limitation conditions imposed in this in vitro assay induce changes in MDH or LDH protein structures, which correlate with enzyme inactivation. It is also shown that plant, fungal and bacterial hydrophilins are able to protect enzymatic activities from water-loss effects in this in vitro system, in a wide range of water potentials. In addition, the data in this work indicate that the presence of hydrophilins also avoids the MDH and LDH conformational modifications caused during the assay. These results show that hydrophilins are able to protect enzymatic activities from inactivation due to in vitro partial water limitation and thus suggest a function for these proteins in vivo. Key-words: dehydrins; enzyme protection; hydrophilic proteins; hydrophilins; LEA proteins; protein stabilization; water deficit.