Figure 1: Structures of sTfR expression vectors and identification of sTfR expression. (a) The wild-type or codon-optimized sTfR gene expression vectors, pcDNA3.1A-CD5-sTfRw/His and pcDNA3.1A-CD5-sTfRopt/His, in which sTfR gene driven by CMV promoter was fused by human CD5 signal peptide sequence at 5′-terminus and 6 × His-tag at 3′-terminus. (b) Identification of sTfR with SDS-PAGE: lane M, protein markers; lane 1, purified sTfR. (c) Identification of sTfR with Western blot: lane M, prestained protein markers; lane 1, sTfR protein expressed from pcDNA3.1A-CD5-sTfRopt/His-transfected cells; lane 2, negative control from empty vector-transfected cells.