Characterization of PEDV/S(1–1320) + CMP + Tags protein. A Purification of the S protein from the silkworm serum. Two-step affinity chromatography using HisTrap excel column and STREP-tactin column was executed described in the Materials and Methods. Lanes 1 and 6, molecular weight marker; lanes 2–5, nickel affinity chromatography; lanes 7–10, STREP-tactin affinity chromatography. All samples were resolved in 8% SDS-PAGE and visualized by CBB staining. An orange arrow indicates the PEDV S protein. B Blue-Native PAGE analysis of the S protein. After electrophoresis, the gel was further stained by CBB. An orange arrow indicates the PEDV S protein trimer. C Size-exclusion chromatography of PEDV S protein. The chromatogram of the S protein is shown as a blue curve. The molecular weight markers are indicated as dashed lines. D The size changes of the S protein against heating. The thermal stability profile was collected by DLS.