Plasma protease C1 inhibitor, also known as SERPING1, is a member of the serpin superfamily of serine protease inhibitors. SERPING1 regulates the activation of complement factor C1 as well as the activity of activated C1 by coupling with the active catalytic site at the light chains of C1r and C1s. Therefore, it plays an important role in regulating activation of both the complement and contact systems. SERPING1 deficiency results in hereditary angioedema, which is characterized by recurrent episodes of localized angioedema of the skin, gastrointestinal mucosa or upper respiratory mucosa. Recombinant human SERPING1 protein, fused to His-tag at N-terminus, was expressed in E.coli.