PROS1 and viral infectious disease: ACE2-Fc inhibits the binding of WT S protein to immobilized ACE2 far more potently than it inhibits binding of S protein stabilized in the prefusion state, consistent with the hypothesis that ACE2 decoys inhibit viral infection not only through competitive inhibition of the S protein–ACE2 interaction but also by triggering the irreversible refolding of the S protein from the prefusion state to the postfusion state.