Chaperone-like activity of human haptoglobin: Similarity with alpha-crystallin

Human haptoglobin (Hp) has been shown to have chaperone-like activity in pr eventing thermally induced aggregation of catalase and gamma-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 gam ma-crystallin from aggregation by oxidative stress. In addition, haptoglobi n also provides protection against glycation-induced inactivation of catala se by glyceraldehyde. Chaperone-like activity of haptoglobin decreases in t he course of its glycation. Refolding studies have shown that Hp exhibits i ts chaperone-like activity predominantly on the unfolding and not on the re folding pathway. Although Hp and alpha-crystallin have no sequence similari ties, it seems that their chaperone-like activities are of the same type.