Molecular characterization of pregnancy‐associated plasma protein‐A by electrophoresis

Abstract

Gradient polyacrylamide gel electrophoresis, isoelectric focusing and multidimensional immunoelectrophoretic techniques have been applied in order to physico-chemically characterize pregnancy-associated plasma protein-A (PAPP-A). By lectin affinity immunoelectrophoresis, PAPP-A contained sialic acid, glucose/mannose and N-acetyl-alpha-D-galactosamine. Immunoelectrophoretic analyses after incubation with various glycolases confirmed these findings and demonstrated that PAPP-A contained glucuronic acid, perhaps in chondroitin sulphate moities, thus indicating that PAPP-A may be a proteoglycan rather than a glycoprotein. Analysis by metal chelate and dye ligand affinity immunoelectrophoresis demonstrated many similarities between PAPP-A and alpha 2-macroglobulin (alpha 2M). However, unlike alpha 2M, PAPP-A did not form immunologically reactive complexes when incubated with proteases. Furthermore, as demonstrated by autoradiographic studies, PAPP-A did not contain internal thiolester groups, thus indicating that PAPP-A cannot inhibit proteases by molecular entrapment and, despite the homotetrameric molecular conformation, PAPP-A and alpha 2M may not have evolved from a common ancestral protein.

The role of PAPP-A in the IGF system: location, location, location

“…Following its discovery, several biological roles of PAPP-A were proposed, including a function as a proteinase inhibitor, inspired by similarities with α-2-macroglobulin (α 2 M) and pregnancy zone protein (PZP) (Sinosich 1990). However, no consensus was established regarding its biological role or subunit organization.…”

“…The first 25 years of PAPP-A -a useful protein of unknown function Human pregnancy-associated plasma protein-A (PAPP-A) was identified 40 years ago as a protein present abundantly in plasma of pregnant women (Lin et al 1974). Following its discovery, several biological roles of PAPP-A were proposed, including a function as a proteinase inhibitor, inspired by similarities with α-2-macroglobulin (α 2 M) and pregnancy zone protein (PZP) (Sinosich 1990). However, no consensus was established regarding its biological role or subunit organization.…”

Expression of Recombinant Human Pregnancy-associated Plasma Protein-A and Identification of the Proform of Eosinophil Major Basic Protein as Its Physiological Inhibitor

“…The concentration in serum reaches about 50 mg/liter at the end of pregnancy (2,3). PAPP-A was originally characterized as a high molecular weight homotetramer (1,4,5), but it has now been demonstrated that PAPP-A exists in pregnancy serum as a covalent, heterotetrameric 2:2 complex with the proform of eosinophil major basic protein (proMBP), PAPP-A/proMBP (6). The presence of proMBP in the circulation, as well as the existence of the PAPP-A/proMBP complex was revealed, in part, by the isolation of a PAPP-A and a proMBP peptide, linked together by a disulfide bond, from a digest of purified PAPP-A/proMBP (6).…”

Association of Low Maternal Pregnancy-associated Plasma Protein A with Adverse Perinatal Outcome

“…Although the PAPP-A mRNA can be found in many tissues, the placental production exceeds any other. The syncytiotrophoblast composes the PAPP-A subunit, while proMBP is synthesized in extravillous trophoblasts, and the two subunits are combined to create the final complex at the extracellular environment [3].…”