title: Quantitative Correlation between Infectivity and Gp120 Density on HIV-1 Virions Revealed by Optical Trapping Virometry.
abstract: The envelope glycoprotein (Env) gp120/gp41 is required for HIV-1 infection of host cells. Although in general it has been perceived that more Env gives rise to higher infectivity, the precise quantitative dependence of HIV-1 virion infectivity on Env density has remained unknown. Here we have developed a method to examine this dependence. This method involves 1) production of a set of single-cycle HIV-1 virions with varied density of Env on their surface, 2) site-specific labeling of Env-specific antibody Fab with a fluorophore at high efficiency, and 3) optical trapping virometry to measure the number of gp120 molecules on individual HIV-1 virions. The resulting gp120 density per virion is then correlated with the infectivity of the virions measured in cell culture. In the presence of DEAE-dextran, the polycation known to enhance HIV-1 infectivity in cell culture, virion infectivity follows gp120 density as a sigmoidal dependence and reaches an apparent plateau. This quantitative dependence can be described by a Hill equation, with a Hill coefficient of 2.4 ± 0.6. In contrast, in the absence of DEAE-dextran, virion infectivity increases monotonically with gp120 density and no saturation is observed under the experimental conditions. These results provide the first quantitative evidence that Env trimers cooperate on the virion surface to mediate productive infection by HIV-1. Moreover, as a result of the low number of Env trimers on individual virions, the number of additional Env trimers per virion that is required for the optimal infectivity will depend on the inclusion of facilitating agents during infection.
authors.affiliation: From the Department of Pharmaceutical Sciences, College of Pharmacy, and.
authors.forename: Michael C
authors.initials: MC
authors.lastname: DeSantis
authors.affiliation: From the Department of Pharmaceutical Sciences, College of Pharmacy, and.
authors.forename: Jin H
authors.initials: JH
authors.lastname: Kim
authors.affiliation: From the Department of Pharmaceutical Sciences, College of Pharmacy, and.
authors.forename: Hanna
authors.initials: H
authors.lastname: Song
authors.affiliation: the Department of Microbiology and Immunology, Weill Cornell Medicine, Cornell University, New York, New York 10065.
authors.forename: Per Johan
authors.initials: PJ
authors.lastname: Klasse
authors.affiliation: From the Department of Pharmaceutical Sciences, College of Pharmacy, and Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48109 and chengwe@umich.edu.
authors.forename: Wei
authors.identifier: 0000-0003-0332-1566
authors.initials: W
authors.lastname: Cheng
mesh_terms: D057809:HEK293 Cells; D015699:HIV Envelope Protein gp120 / Q000378:metabolism*; D015658:HIV Infections / Q000821:virology*; D015497:HIV-1 / Q000378:metabolism / Q000472:pathogenicity*; D006801:Humans; D052898:Optical Tweezers; D014771:Virion / Q000378:metabolism / Q000472:pathogenicity*; D014774:Virulence
chemical_list: D015699:HIV Envelope Protein gp120
keywords: glycoprotein; human immunodeficiency virus (HIV); infection; optical tweezers; protein cross-linking; single particle analysis; single-molecule biophysics