Maspin binds to urokinase-type and tissue-type plasminogen activator through exosite-exosite interactions.

Maspin is a member of the serpin family with a reactive center loop that is incompatible with proteinase inhibition by the serpin conformational change mechanism. Despite this there are reports that maspin might regulate uPA-dependent processes in vivo. Using exogenous and endogenous fluorescence, we demonstrate here that maspin can bind uPA and tPA in both single-chain and double-chain forms, with K(d) values between 300 and 600 nM.

Crystal structure of human maspin, a serpin with antitumor properties: reactive center loop of maspin is exposed but constrained.

Maspin, a member of the serpin superfamily, has tumor suppressing activity against breast and prostate cancer. Maspin inhibits tumor growth by blocking cell invasion, and its reactive center loop (RCL) is thought to mediate this activity. To understand this function on the molecular level, we have solved the three-dimensional structure of Maspin to 3.