ASR1 folding is modulated by its intrinsically disordered protein properties upon saline and osmotic stress.

WETZLER, D. E.; RINALDI, J.; RICARDI, M.M.; BUCCI, H.A.; IUSEM, N. D.; UCHS WIGHTMAN, F; CARAMELO J.J.

Ciudad Autónoma de Buenos Aires

Congreso; Reunión Conjunta de Biociencias; 2017

Plant species in arid zones are constantly exposed to drought stress. The ASR protein family (Abscisic, Stress, Ripening) -a subgroup of the late embryogenesis abundant superfamily- is involved in the water stress response and adaptation to dry environments. Tomato ASR1, as well as other members of this family, is an intrinsically disordered protein (IDP). We employed different biophysical techniques to perform a deep in vitro characterization of ASR1 as an IDP and showed how both environmental factors and in vivo targets are related to its folding. We present evidence that ASR1 exhibits the plasticity to easily adopt different conformations like the α-helix or polyproline type II (PII) depending on the surroundings. Low temperatures and low pH, promote ASR1 to partially fold in a PII conformation. Whereas NaCl diminishes PII content and slightly stabilized α-helix conformation, PEG and glycerol had1an important effect stabilizing α-helix conformation. We also found that Zn2+ binding to ASR1 in the low micromolar range promotes folding to α-helix while extra Zn2+ results in homo-dimerization. ASR1-DNA binding showed to be DNA-sequence specific and dependent on Zn2+. We designed a FRET reporter to sense ASR1 folding in vivo. Its effectiveness was confirmed in the heterologous model organism Escherichia coli under saline and osmotic stress conditions. The designed sensor represents a promising probe to be used in plant cells. Overall, this work supports the notion that ASR1 plasticity is a key feature that facilitates its response to drought stress and the interaction with its specific targets.