FC0079
Anhydrin  -  Polyadenylate binding protein 2 (PABPN1-A17)

Biological function
Highly hydrophilic proteins as a major component of the response to extreme water stress. Anhydrin, whose gene is induced in response to dehydration in the anhydrobiotic nematode, Aphelenchus avenae and does not belong to the embryogenesis abundant (LEA) proteins.

Structural evidence
Evidence from in vivo FRET experiments for a degree of association between anhydrin and PABPN1-A17 consistent with weak and/or short-lived complex formation. This indicates that anhydrin does not function exclusively as an entropic chain, by a volume exclusion effect, but rather can interact loosely with client proteins to provide an electrostatic and/or steric obstacle to close approach of other aggregating species. Aggregation reducing activity may result from electrosteric interference where the IDP reduces the encounter frequency of aggregating protein species, termed as molecular shield activity.

Biochemical evidence
The enzyme citrate synthase (CS) was dried in the presence of anhydrin, a significant decrease in aggregation was observed. In the nucleus nuclear polyadenine binding protein with 17 consecutive alanine residues (EGFP-PABPN1-A17) was used to test for antiaggregation activity and supported a protein antiaggregation role for anhydrin in vivo. Coimmunoprecipitation suggests that this association is not strong, it is possible that anhydrin interacts more loosely with its targets.

Mechanism category
tethering, shielding

Significance
Fuzziness and dynamic assembly of anhydrin with its clients could provide electrostatic shielding and prevent aggregation. It can also help dissociation from the partner.