Structure-based internal deletions of HPV16 L1. A) Sequence alignment of HPV 16 and HPV18 L1, showing the conserved regions of h2, h3, and h4. B) Diagram showing the design of the four internal deletions of HPV16 L1. D1 has a deletion within h4 and D2 removes h4 and a few residues outside the boundaries of h4 on both ends. C) Solubility and stability of the four constructs of HPV16 L1. Lanes 2–4: D1-L1 mutant; lanes 5–7: D2-L1 mutant; lanes 8–10: D3-L1 mutant; and lanes 11–12: D4-L1 mutant. Lanes 2, 5, 8, and 11 show the proteins eluted from the resin before thrombin digestion; lanes 3, 6, and 9 show the proteins eluted from the column after thrombin digestion; and lanes 4, 7, 10, and 12 show the proteins in the resin after thrombin digestion and elution. D) Size-exclusion chromatography analysis of the D1-L1 eluted from the column after thrombin treatment, showing the typical elution profile on Superdex-200. The major peak has an apparent molecular weight of ~235 kD, the expected size for a pentameric L1.