Fig 4. Morphologies and mechanical properties of HIV-1 capsids from AFM.

(a) The average stiffness of isolated WT HIV-1 capsids in the absence (n = 30) and presence (n = 36) of IP₆. Error bars indicate SEM. Statistical significance was confirmed using the Mann–Whitney U test for p < 0.05. (b) Average stiffness of HIV-1 capsids treated with 100 μM IP₆ (black) or BHC (orange) as a function of time after the addition of dNTPs and MgCl₂. The red diamond represents the average stiffness of WT capsids before addition of IP₆ or BHC. The initial average stiffness, at time 0, was measured before addition of dNTPs and MgCl₂. At each time point, the stiffness of 2 to 4 capsids was measured without stopping the reaction. WT data (taken from [17]) is presented as a gray line for comparison. The error bars represent SEM. (c) A representative cone-shaped capsid (of 20 imaged) prior to addition of dNTP and MgCl₂. (d–f) Deformed and damaged capsids visualized after 5 h. For clarity, openings in the capsids are shown within a dashed yellow rectangle. Scale bars, 50 nm. A total of 52 capsids were visualized. (Approximately 400 force-distance curves were obtained from individual capsids). Numerical data for panel A and B can be found in S4 Data. AFM, atomic force microscopy; BHC, benzenehexacarboxylic acid; dNTP, deoxynucleotide triphosphate; IP₆, inositol hexakisphosphate; WT, wild-type.