Antibodiesand Their Recognition by Immunotypes of a Quaternary Site of HIV-1

HIV-1 is neutralized by a class of antibodies that preferentially recognize a site formed on the assembledviralspike.Suchquaternarystructure-specificantibodieshavediverseneutralizationbreadths,withantibodiesPG16 and PG9 able to neutralize 70 to 80% of circulating HIV-1 isolates while antibody 2909 is specific forstrain SF162. We show that alteration between a rare lysine and a common N-linked glycan at position 160 ofHIV-1 gp120 is primarily responsible for toggling between 2909 and PG16/PG9 neutralization sensitivity.Quaternary structure-specific antibodies appear to target antigenic variants of the same epitope, with neu-tralization breadth determined by the prevalence of recognized variants among circulating isolates.