title: Adoption of an "open" envelope conformation facilitating CD4 binding and structural remodeling precedes coreceptor switch in R5 SHIV-infected macaques.
abstract: A change in coreceptor preference from CCR5 to CXCR4 towards the end stage disease in some HIV-1 infected individuals has been well documented, but the reasons and mechanisms for this tropism switch remain elusive. It has been suggested that envelope structural constraints in accommodating amino acid changes required for CXCR4 usage is an obstacle to tropism switch, limiting the rate and pathways available for HIV-1 coreceptor switching. The present study was initiated in two R5 SHIV(SF162P3N)-infected rapid progressor macaques with coreceptor switch to test the hypothesis that an early step in the evolution of tropism switch is the adoption of a less constrained and more "open" envelope conformation for better CD4 usage, allowing greater structural flexibility to accommodate further mutational changes that confer CXCR4 utilization. We show that, prior to the time of coreceptor switch, R5 viruses in both macaques evolved to become increasingly sCD4-sensitive, suggestive of enhanced exposure of the CD4 binding site and an "open" envelope conformation, and this correlated with better gp120 binding to CD4 and with more efficient infection of CD4(low) cells such as primary macrophages. Moreover, significant changes in neutralization sensitivity to agents and antibodies directed against functional domains of gp120 and gp41 were seen for R5 viruses close to the time of X4 emergence, consistent with global changes in envelope configuration and structural plasticity. These observations in a simian model of R5-to-X4 evolution provide a mechanistic basis for the HIV-1 coreceptor switch.
authors.affiliation: Aaron Diamond AIDS Research Center, New York, New York, United States of America.
authors.forename: Ke
authors.initials: K
authors.lastname: Zhuang
authors.forename: Andres
authors.initials: A
authors.lastname: Finzi
authors.forename: Silvana
authors.initials: S
authors.lastname: Tasca
authors.forename: Madina
authors.initials: M
authors.lastname: Shakirzyanova
authors.forename: Heather
authors.initials: H
authors.lastname: Knight
authors.forename: Susan
authors.initials: S
authors.lastname: Westmoreland
authors.forename: Joseph
authors.initials: J
authors.lastname: Sodroski
authors.forename: Cecilia
authors.initials: C
authors.lastname: Cheng-Mayer
mesh_terms: D000818:Animals; D015704:CD4 Antigens / Q000737:chemistry* / Q000378:metabolism*; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology / Q000821:virology; D018450:Disease Progression; D015699:HIV Envelope Protein gp120 / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008251:Macaca / Q000276:immunology / Q000821:virology*; D008264:Macrophages / Q000821:virology; D009500:Neutralization Tests; D011485:Protein Binding; D019713:Receptors, CCR5 / Q000378:metabolism*; D019718:Receptors, CXCR4 / Q000378:metabolism*; D016097:Simian Acquired Immunodeficiency Syndrome / Q000276:immunology / Q000821:virology*; D015302:Simian Immunodeficiency Virus / Q000502:physiology*; D012995:Solubility; D013997:Time Factors; D018523:Tropism; D053586:Virus Internalization
chemical_list: D015704:CD4 Antigens; D015699:HIV Envelope Protein gp120; D019713:Receptors, CCR5; D019718:Receptors, CXCR4