Author contributions
Y.W. and W.H. conceived, designed, and supervised the experiments; M.C. performed the neutralization assays; Z.H., J.Q., G.L. and F.Y. performed 12-2A12 crystallization, data collection and structure determination. Y.Y., T.M. and Y.L completed 12-2A12 isolation and affinity determination. M.C. and Z.H. wrote the manuscript; All authors approved the final manuscript.