PROS1 and infection: To determine whether the combination of HR2P-M2 and m336 also exhibited synergistic antiviral activity against infection of MERS-CoV strains with mutations in RBD or in the HR1 domain, we constructed pseudoviruses bearing MERS-CoV S protein with mutations in RBD, including D509G, D510G, Q522H, or I529T, and those in the HR1 domain, including Q1020H and Q1020R [25,26].