CLPB3 FROM ARABIDOPSIS THALIANA DISPLAYS CHAPERONE ACTIVITY PER SE

PARCERISA, IVANA L.; ROSANO, GERMÁN L.; CECCARELLI, EDUARDO A.

Buenos Aires

Congreso; REUNIÓN CONJUNTA DE SOCIEDADES DE BIOCIENCIAS; 2017

SOCIEDADES DE BIOCIENCIAS

All cells have developed a protein network involved inmaintaining the proteome homeostasis, particularly after periods ofstress. When massive protein aggregation occurs due to heat exposure,cell survival relies on the ClpB/Hsp100 subfamily of molecularchaperones which promote the solubilization and reactivation of proteinaggregates. The bacterial chaperone ClpB and its homologue inyeast, Hsp104 are the most extensively studied disaggregases. Likemany members of the AAA+ superfamily, ClpB/Hsp104 protomersform ring-like homohexameric complexes.The mechanical energynecessary to disentangle protein aggregates is provided by ATP hydrolysisat the two nucleotide-binding domains of each monomer.ClpB and Hsp104 collaborate with the DnaK or Hsp70 chaperonesystem, respectively, to dissolve protein aggregates both in vivo andin vitro, with DnaK/Hsp70 playing a main function in the regulationof ClpB/Hsp104 activity. In the present study, we have exploredthe substrate recognition by ClpB from A. thaliana chloroplasts(AtClpB3) and the role of its cpHsp70 chaperones in this recognition.We demonstrated that AtClpB3 ATPase activity is stimulatedby caseins, poly-lysine and glucose-6-phosphate dehydrogenase(G6PDH) aggregates, but not by luciferase aggregates. In addition,cpHsp70s did not enhance AtClpB3 activity, albeit the presence ofcaseins. Likewise, AtClpB3 could mediate G6PDH disaggregationindependently from cpHsp70 chaperones, recovering the activity ofthe denatured enzyme up to a 65 %. Besides, it has distinct propertiesnot previously reported for Hsp104 or ClpB, as it interactsmore efficiently with the aggregated G6PDH in the presence of thenon-hydrolysable ATP analog AMP-PNP rather than ATPγS. This isthe first evidence that a ClpB disaggregating activity can be exertedwithout the participation of other proteins and establishes a first approachto understanding AtClpB3 substrate preferences.