Figure 5.

The location of the amino acid differences between the SP-A1 and SP-A2 genetic variants as well as the amino acid differences among variants are shown on the different SP-A protein regions (signal peptide, N-terminal, collagen-like, neck, and carbohydrate recognition domain (CRD)). The black arrows show the gene specific differences where all the SP-A1 variants differ from all the SP-A2 variants. The blue and red arrows show differences in SP-A2 and SP-A1 variants, respectively. Residue 85 is noted for its importance in function and biochemical properties between SP-A1 and SP-A2. After the signal peptide is removed, as shown, some of the variants become identical in their coding region.