Enhanced Yield and Gentle Purification of HIV for Cryo-Electron Tomography Analysis of Virion Maturation

HIV is a lentivirus characterized by the formation of its mature core. Visualization and structural examination of HIV requires purification of virions to high concentrations. The yield and integrity of these virions are crucial for ensuring a uniform representation of all viral particles in subsequent analyses. In this study, we present a method for purification of HIV virions which minimizes forces applied to virions while maximizing the efficiency of collection. This method allows us to capture between 1,000 and 5,000 HIV virions released from individual HEK293 cells after transfection with the NL4.3 HIV backbone, a 10 fold advantage over other methods. We utilized this approach to investigate HIV core formation from several constructs: pNL4-3(RT:D ₁₈₅ A&D ₁₈₆ A) with an inactive reverse transcriptase, NL4.3(IN: V ₁₆₅ A&R ₁₆₆ A) with a type-II integrase mutation, and NL4.3(Ѱ: Δ(105-278)&Δ(301-332)) featuring an edited Ѱ packaging signal. Notably, virions from NL4.3(Ѱ: Δ(105-278)&Δ(301-332)) displayed a mixed population, comprising immature virions, empty cores, and cores with detectable internal density. Conversely, virions derived from NL4.3(IN: V ₁₆₅ A&R ₁₆₆ A) exhibited a type II integrase mutant phenotype characterized by empty cores and RNP density localized around the cores, consistent with previous studies. In contrast, virions released from pNL4-3(RT:D ₁₈₅ A&D ₁₈₆ A) displayed mature cores containing detectable RNP density. We suggest that the purification methods developed in this study can significantly facilitate the characterization of enveloped viruses.