Our group was the first to show a relationship between allostery in GroEL and GroEL-assisted protein folding rates (Yifrach and Horovitz, 2000). Using different cooperativity mutants of GroEL, we found a linear relationship between the folding rate of mouse dihydrofolate reductase (under conditions where its folding is GroEL-dependent but GroES-independent) and the rate and Hill coefficient of the T→R allosteric transition.
The atomic-resolution structures of the relatively stable (T and R) end states of several allosteric proteins are known but the pathways by which they interconvert are generally not known. We addressed this issue using GroEL as a model system by employing linear free energy relationships of physical organic chemistry such as phi-value analysis (Yifrach and Horovitz, 1998) ; Horovitz et al, 2002), double-mutant cycles (Horovitz, 1996) and correlated mutation analysis (Kass and Horovitz, 2002; Noivirt et al., 2005).
The unique hetero-oligomeric structure of CCT/TRiC is thought to be responsible for many of the properties that distinguish it from GroEL such as the combinatorial nature of protein substrate binding by specific subunits and its sequential intra-ring allostery. In order to test the functional significance of the hetero-oligomeric structure, we generated a set of yeast strains with an identical mutation in each of the CCT/TRiC subunits, in turn, at a position that is conserved in all the subunits and is involved in ATP hydrolysis (Amit et al., 2010).
It is unclear why some proteins need GroE for correct folding and others do not. Computational studies have shown that obligatory substrates, for example, have lower folding propensities and are more aggregation-prone (Azia et al., 2012).