4I3S:
reference: Outer domain of HIV-1 gp120: Antigenic optimization, structural malleability, and crystal structure with antibody VRC-PG04., Joyce MG, Kanekiyo M, Xu L, Biertumpfel C, Boyington JC, Moquin S, Shi W, Wu X, Yang ZY, Yang Y, Zhang B, Zheng A, Zhou T, Zhu J, Mascola JR, Kwong PD, Nabel GJ, J Virol. 2012 Dec 12. PMID: 23236069

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