a, Purified MPRLV VLPs (8 μg protein) bearing an N-terminal StrepTag were resolved on an SDS–polyacrylamide gel and visualized by Coomassie blue staining. R, reducing conditions; NR, nonreducing conditions. b, MPRLV VLPs were negatively stained with uranyl acetate and visualized by electron microscopy. c, Kinetic constants for MPRLV VLP-sEC1–2 interaction were determined by biolayer interferometry. kon, association-rate constant; koff, dissociation rate constant. Values ± 95% confidence intervals derived from curve fits are shown for two independent experiments. These experiments were performed three times with similar results.