Fig 1: Comparison of human Aß, human IAPP and rodent IAPP peptide sequences.(A) The amino acid sequence of human Aß (10–42); the described “theta” site (?) is indicated by an arrow between phenylalanine residues 19 and 20 (in red). (B) The amino acid sequence of mature human IAPP; phenylalanine residues at positions 15 and 23 (in red). The potential peptide fragment species induced by BACE2-mediated cleavage are indicated: 1–37, 1–15, 16–23, 24–37, 1–23, and 16–37. (C) The amino acid sequence of mature rodent IAPP; the phenylalanine residue at position 15 (red) and residue differences between human and rodent sequences (blue) are highlighted.
Fig 2: BACE2-mediated proteolytic cleavage of hIAPP is blocked by insulin but not proinsulin.(A) MS analysis of hIAPP incubated with recombinant BACE2; the predicted peaks are indicated: 1–37, 24–37, 1–15, 16–37 and 1–23. (B) Co-incubation with recombinant human insulin blocks BACE2-mediated digestion of hIAPP. (C) Co-incubation with recombinant human proinsulin does not prevent BACE2-mediated digestion of hIAPP. (D) hIAPP plus recombinant human insulin: Single protonated IAPP (m/z 3903) and double protonated IAPP (m/z 1952); single protonated insulin (m/z 5806) and double protonated insulin (m/z 2903). (E) hIAPP plus recombinant human proinsulin; single protonated IAPP (m/z 3903), double protonated IAPP (m/z 1952), double protonated proinsulin (m/z 5250), triple protonated proinsulin (m/z 3495), and quadruple protonated proinsulin (m/z 2625). (F) Recombinant insulin is unchanged by recombinant BACE2. (G) Recombinant proinsulin is unchanged by recombinant BACE2. (H) Recombinant insulin alone and (I) recombinant proinsulin alone. All reactions were performed in PBS, pH 7 for 4 hours at 37°C. Peptide fragment sequences detailed in Table 4.
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