THE INTRINSICALLY DISORDERED PROTEIN-PROPERTIES OF THE PLANT PROTEIN ASR1 ARE CLOSELLY RELATED TO ITS FUNCTION AS A DROUGHTSTRESS-RESPONSIVE TRANSCRIPTION FACTOR

DIANA ELENA WETZLER; FEDERICO FUCHS WIGHTMAN; HERNAN ANDRES BUCCI; JIMENA RINALDI; JULIO JAVIER CARAMELO; NORBERTO DANIEL IUSEM ; MARTINIANO MARIA RICARDI

Buenos Aires

Congreso; Reunión Conjunta de Sociedades de Biociencias; 2017

Reunión Conjunta de Sociedades de Biociencias

Plant species in arid zones areconstantly exposed to droughtstress. The ASR (Abscisic, Stress, Ripening)protein family- a subgroup of the late embryogenesis abundant (LEA)superfamily- is involved in the water stress response and adaptation to dryenvironments. Tomato ASR1, as well as other members of this family, is predictedto be an intrinsically disordered protein (IDP). In this context, we employedbiophysical techniques to perform a deep in vitro characterization of ASR1 asan IDP protein and showed how both environmental factors and in vivo targetsare related to its folding. We present evidence supporting that ASR1 is an IDPand exhibits the plasticity to easily adopt different conformations like theα-helix or polyproline (PII) depending on the surroundings (G~1 kcal/mol). Wealso show that environmental changes like low temperatures and low pH promoteASR1 to be partially folded in a PII conformation. Interestingly, the additionof agents that mimic abiotic stress conditions causes different effects on ASR1secondary structure. While NaCl diminishes PII content, PEG and glycerolstabilize theα-helix conformation. In addition, we found that Zn2+binding toASR1with a defined stoichiometry promotes its folding to α-helix [Kd= (1.3±0.2) µM]. Extra Zn2+ binding promotes dimerization. Moreover, the binding ofstoichiometric Zn2+ is necessary for binding its specific target DNA with a 1:1stoichiometry [Kd= 216± 10) nM], with a 5-foldpreference over the scrambledsequence oligonucleotide. Furthermore, we designed a FRET reporter to senseASR1 folding in vivo. In order to assess its effectiveness, we expressed thisprotein sensor in E. coli and tested it under saline and osmotic stress. Overall,this work supports the notion that plasticity of ASR1 is a key feature thatfacilitates its response to drought stress and the interaction with its specifctargets.