Hydrophilins from distant organisms can protect enzymatic activities from water limitation effectsin 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‐Arroyoet al.,Journal of Biological Chemistry275, 5668–5674, 2000). To gain insight into the function of hydrophilins, anin vitroassay 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 1‐anilinonaphtalene‐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 thisin vitroassay 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 thisin vitrosystem, 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 toin vitropartial water limitation and thus suggest a function for these proteinsin vivo.