Cystatin domains in alpha‐2‐HS‐glycoprotein and fetuin

Abstract

We have found that chain A of alpha‐2‐HS‐glycoprotein contains two cystatin domains that show closest similarity to those of kininogen. Most likely, the two proteins diverged after the primary duplication of a single cystatin domain as the two cystatin domains of alpha‐2‐HS‐glycoprotein are more similar, especially in disulfide bonding, to the corresponding domains of kininogen than to each other. We also propose that the carboxyl‐terminal (non‐cystatin) parts of kininogen and alpha‐2‐HS‐glycoprotein contain homologous segments. We suggest that alpha‐2‐HS‐glycoprotein may act as an inhibitor of the cysteine proteinases responsible for bone resorption. We have also found that fetuin is closely related to alpha‐2‐HS‐glycoprotein.