Structural comparison and modular organization of DBLMSP1 and DBLMSP2. (A) Domain structure of DBLMSP1 (PF3D7_1035700) annotated in PlasmoDB, showing the Duffy-antigen binding domain (residues ~553–930) and the Merozoite SPAM domain (~1624–2088). (B) Modular segmentation of DBLMSP1 based on sequence alignment. The structure includes an upstream conserved region (1CM_up), four variable modules (1M1–1M4, with 1M1 and 1M4 highlighted as highly polymorphic), and a downstream conserved region (1CM_down). (C) Domain structure of DBLMSP2 (PF3D7_1036300) showing a similar organization with a DBL domain (~601–1023) and a SPAM domain (~1711–2286). (D) Modular segmentation of DBLMSP2 includes an upstream conserved region (2CM_up), five variable modules (2M1–2M5), and a downstream conserved region (2CM_down). A short insertion (~12 bp) was observed downstream of the SPAM domain in some variants. Shared modules between DBLMSP1 and DBLMSP2 (e.g., 1M3 and 2M5) indicate historical recombination and intertypic exchange.