Crystal structure of constitutively monomeric E. coli Hsp33 mutant with chaperone activity.

Heat shock protein 33 (Hsp33) from Escherichia coli is a redox-regulated molecular chaperone that protects cells from oxidative stress. To understand the molecular basis for the monomer–dimer switch in the functional regulation of E. coli Hsp33, we generated a constitutively monomeric Hsp33 by introducing the Q151E mutation in the dimeric interface and determined its crystal structure. The overall scaffold of the monomeric Hsp331–235 (Q151E) mutant is virtually the same as that of the dimeric form, except that there is no domain swapping. The measurement of chaperone activity to thermally denatured luciferase showed that the constitutively monomeric Hsp33 mutant still retains chaperone activity similar to that of wild-type Hsp331–235, suggesting that a Hsp33 monomer is sufficient to interact with slowly unfolded substrate.