Late Embryogenesis Abundant (LEA) proteins comprise a heterogeneous group of proteins that accumulate to high levels in the dry seed and in vegetative plant tissues under water deficit. We recently reported that group 4 LEA proteins from Arabidopsis thaliana, regardless of their structural disorder prevalent in aqueous solution, are able to fold into α-helix when subjected to water deficit and/or macromolecular crowding environments. Interestingly, the ability to gain structure under water limiting conditions is circumscribed to the N-terminal conserved region. This environment- driven conformational plasticity has a functional impact because the conserved N-terminal region is necessary and sufficient to prevent the inactivation and/or aggregation of reporter enzymes, when they are subjected to partial dehydration or freeze-thaw treatments. In this addendum we present a broader analysis of the data and propose that the mechanism by which group 4 LEA proteins exert their chaperone-like activity occurs via a selection of particular LEA structural conformations favored by water deficit environments. In addition, we include further observations regarding the abundance and conservation of histidine residues in LEA proteins of this group, particularly at the C-terminal variable region, supporting the presence of an additional function in the same polypeptides as metal ion sequesters. The structural characteristics of group 4 LEA proteins together with their conceivable multifunctionality, a widespread feature in Intrinsically Disordered Proteins (IDPs), raises the possibility of using this set of proteins as a model to investigate the structure-function relationship of IDPs in plants.
Keywords: Intrinsically disordered proteins; late embryogenesis abundant proteins; plant molecular biology; protein folding; protein structure; stress response; water deficit.