GASP‐1 and GASP‐2, two closely structurally related proteins with a functional duality in antitrypsin inhibition specificity: a mechanistic point of view.

While GASP‐1 and GASP‐2 proteins are known to regulate myogenesis by inhibiting myostatin, their structural organization suggests a putative role as multivalent protease inhibitors controlling different protease activities. In this study, we show the noncompetitive and competitive antitrypsin activities of the full‐length GASP‐1 and GASP‐2 proteins, respectively, by using a bacterial system production and in vitro enzymatic experiments. The role of the second Kunitz domain in this functional duality is described by assessing the antitrypsin activity of GASP‐1/2 chimeric proteins. Molecular dynamics simulations support the experimental data to rationalize differences in binding modes between trypsin and the GASP‐1 and GASP‐2 second Kunitz domains. A new inhibition mechanism was evidenced for the second Kunitz domain of GASP‐2, in which the conventional cationic residue of trypsin inhibitors was substituted by the strongly interacting glutamine residue. [ABSTRACT FROM AUTHOR]