Human Pappalysin‑1/PAPP‑A Alexa Fluor™ Plus 488‑conjugated Antibody

Pappalysins belong to a fifth family of metzincins that consists of ADAMs/ADAMTSs, MMPs, astacins and serrylysins (1). PAPP-A is an important pregnancy protein and increases in plasma by a factor of about 150 during pregnancy as compared to the nonpregnant state. PAPP-A is also a major marker of Down syndrome in the first trimester of pregnancy because maternal serum levels of PAPP-A are significantly reduced when a fetus affected by Down syndrome is present (2). PAPP-A cleaves Insulin-like Growth Factor-Binding Protein-4 and -5 (IGFBP-4 and -5) at a single site, resulting in the release of bioactive IGF (3). Lack of IGFBP-4 cleavage in embryonic fibroblasts derived from PAPP-A knockout mice indicates that PAPP-A functions as a physiological IGFBP-4 protease (4). Three Lin12-Notch repeats (LNR) in the PAPP-A protein bind Ca²⁺ and are required for the cleavage of IGFBP-4, not IGFBP-5, by PAPP-A (5). The C-terminal LNR (residues 1476 to 1503) is not present in rhPAPP-A (residues 82 to 1214), which starts at the N-terminus of the mature chain and ends before the five Sushi (SCR) modules. As an active protease, rhPAPP-A cleaves IGFBP-5, which can be inhibited by 1,10-phenanthroline.