Chaperone-Like Activity of Human Haptoglobin: Similarity with α-Crystallin

Human haptoglobin (Hp) has been shown to have chaperone-like activity in preventing thermally induced aggregation of catalase and γ-crystallin. No differences in the chaperone- like behaviour of genetic types Hp 1-1 and a mixture of types Hp 2-1 and Hp 2-2 (i.e. Hp II) were found. Haptoglobin not only suppresses heat-induced aggregation of proteins but also prevents γ-crystallin from aggregation by oxidative stress. In addition, haptoglobin also provides protection against glycation-induced inactivation of catalase by glyceraldehyde. Chaperone-like activity of haptoglobin decreases in the course of its glycation. Refolding studies have shown that Hp exhibits its chaperone-like activity predominantly on the unfolding and not on the refolding pathway. Although Hp and α-crystallin have no sequence similarities, it seems that their chaperone-like activities are of the same type.