Journal: Frontiers in Bioengineering and Biotechnology
Article Title: Structure-guided engineering of prototype foamy virus Env identifies key residues for heparan sulfate binding and enhances transduction efficiency
doi: 10.3389/fbioe.2026.1716928
Figure Lengend Snippet: Functional characterization of PFV Env upper domain point mutants affecting HS binding and viral entry efficiency. (A) The structure shown represents the receptor-binding domain (RBD) of the PFV Env surface subunit (SU), modeled using AlphaFold2. The molecular docking pose of heparan sulfate (HS) is displayed on the positively charged pocket of the RBD upper domain (UD), with key interacting residues (R298, R440, and E446) highlighted. The binding free energy which calculated from Autodock-vina, −7.0 kcal/mol is labeled. The molecular docking simulation revealed three key residues, Arg(R)298, Arg(R)440, and Glu(E)446, located in UD. These residues form hydrogen bonding with negatively charged sulfate group of HS and are highlighted in red and cyan for negatively charged and positively charged residues, respectively. Based on this structural analysis, R298A, R440A, and E446A substitutions were designed to disrupt the HS binding. The distance between key residues and HS are labeled with black arrow. (B) Western blot analysis was performed to confirm the protein expression of wild type and Env variants (R298A, R440A, and E446A) in HEK293FT cells. The cells were co-transfected with the PFV transfer vector (v3) and Env plasmids at a 30:1 ratio. All three mutants showed Env protein levels comparable to those of the wild type, indicating that the point mutations did not affect protein expression or stability. β -actin was used as a loading control. Mock, HEK293FT cell line served as a negative control; PC, HEK293FT cells transfected pCMV-Env were used as a positive control. (C) To assess the effect of each Env variant on viral infectivity, supernatants from transfected HEK293FT cells were used to transduce HT1080 cells. Transduction efficiency was monitored by EGFP expression using fluorescence microscopy after 3 days. Phase-contrast images confirmed the equivalent cell density across conditions. Scale bars = 100 μm. (D,E) Flow cytometry was used to quantitatively measure the proportion of EGFP-positive HT1080 cells transduced with each viral construct. Representative histograms and bar graph quantifications ( N ≥ 3) are shown in (D) and (E) , respectively. The average number from at least three independent experiments is shown at the top of each bar. Error bars represent the standard deviation of biological triplicates.
Article Snippet: The human fibrosarcoma cell line HT1080 was obtained from the Korean Cell Line Bank, and the human embryonic kidney cell line HEK293FT was obtained from Thermo Fisher Scientific (USA).
Techniques: Functional Assay, Binding Assay, Labeling, Western Blot, Expressing, Transfection, Plasmid Preparation, Control, Negative Control, Positive Control, Variant Assay, Infection, Transduction, Fluorescence, Microscopy, Flow Cytometry, Construct, Standard Deviation