Fig. 1.

Most primary processing site sequences diverge between the two MSP1 allelic types.Primary proteolytic processing of MSP1 by PfSUB1 results in the production of the MSP1₈₃, MSP1₃₀, MSP1₃₈ and MSP1₄₂ fragments (top centre). The amino acid sequences within which cleavage occurs are shown for the two major dimorphic forms of MSP1, typified by those of the 3D7 and Wellcome isolates (centre). Also shown is an additional cleavage site (called 83int, indicated by dotted lines) that occurs only in the 3D7-type MSP1. The only detected microheterogeneity in the cleavage sites is a Thr-to-Ala substitution in the P4′ position of the 3D7-type 83/30 cleavage site. The positions of the primary cleavage sites relative to the distribution of conserved (open), variable (black) and semi-conserved (grey) blocks within MSP1, numbered 1–17 according to Tanabe et al. (1987) are shown (bottom). The sequence at which PfSUB2-mediated secondary processing occurs is also shown (top right). Note that PfSUB1 cannot cleave C-terminal to a Leu residue, and the secondary processing site is completely refractory to PfSUB1 (Withers-Martinez et al., 2002; Yeoh et al., 2007; Koussis et al., 2009).