Reevaluation of VAR2CSA domain boundaries. A) The disulfide bond structure in four solved DBL domains [5, 8, 16, 17] is shown above the dashed line. An unpaired C10a cysteine residue in EBA175 F1 is italicized. Below the dashed line is the predicted disulfide bonds in VAR2CSA domains. Black cysteines are invariant, grey cysteines were present in more than 50% of sequences from a comparison of 19 var2csa sequences . The location of S1, S2, and S3 subdomains, including anti-parallel α-helical elements in the S3 subdomain are shown. B) VAR2CSA protein schematic showing DBL domains and interdomain (ID) regions. The original DBL domain boundaries are shown in black and numbered according to IT4-VAR2CSA (AAQ73926). Revised domain boundaries including predicted C11 and C12 cysteines are shown in grey. The DBL6 domain has two CX1–2C motifs, either of which may mark the domain end. Cysteine residues are numbered from the protein start and colored black or grey as described above. The three unnumbered cysteine residues are not present in the IT4 VAR2CSA sequence, but were present in more than 50% of VAR2CSA sequences. The location of disulfide bonds in the solved DBL3 domain [5, 8] and the predicted CIDR-like domain [30, 31] are indicated.