Differential acquisition of antigenic peptides by Hsp70 and Hsc70 under oxidative conditions.

Hsp70 and Hsc70 are two chaperones of high homology expressed under contrasting situations. Hsc70 is constitutively expressed and poorly stress-inducible, whereas Hsp70 is unabundant in normal physiological situations and strongly induced under oxidative stress. In the present study we show that the chaperoning activity of purified Hsp70 and Hsc70 is minimal under reducing conditions and increases in environments that mimic oxidative stress. Association with peptides is more pronounced for Hsp70 than for Hsc70 in every condition tested and is accompanied with a gradual change in secondary structure during oxidation. The binding of peptides to Hsp70 and Hsc70 under oxidative conditions is not reversible by treatment with a reducing agent, confirming that other chaperone-associated factors are required for substrate release. These findings support the idea that formation of HSP70-peptide complexes and possibly their immunogenicity is enhanced in conditions of stress.