Improved Supra-Organization Is A Conformational And Functional Adaptation Of Respiratory Complexes

ABSTRACT Multiple surveillance mechanisms accelerate proteasome mediated degradation of misfolded proteins to prevent protein aggregation inside and outside mitochondria. But how cells safeguard mitochondrial function despite increased protein aggregation during proteasome inactivation? Here, using two-dimensional complexome profiling, we extensively characterize the dynamic states of respiratory complexes (RCs) in proteasome-inhibited cells. We report that RC-subunits are increasingly integrated into supra-organizations to optimize catalytic activity simultaneous to their aggregation inside mitochondria. Complex-II (CII) and CV are incorporated into oligomers. CI, CIII, and CIV subcomplexes are associated into holocomplexes followed by integration into supercomplexes. Time-course experiments reveal that the core (CI+CIII 2 ) stoichiometry of supercomplex (I+III 2 +IV) is preserved during early-stress while CIV composition varies. Simultaneously, increased CI-activity suggests conformational optimization of supercomplexes for better function. Re-establishment of steady-state stoichiometry and relative increase in supercomplex-quantity consolidates functional adaptation during prolonged proteasome-inhibition. Together, we name this pre-emptive adaptive mechanism as ‘improved Supra-organization of Respiratory Complexes’ (iSRC). We find that iSRC is active in multiple protein-unfolding stresses, in multiple cell-types that differ in proteostatic and metabolic demands, and reversible upon stress-withdrawal.