Annexin proteins PP4 and PP4-X. Comparative characterization of biological activities of placental and recombinant proteins

The human placental proteins PP4 and PP4-X, belonging to the annexin protein family, were expressed in Escherichia coli at high yield. The proteins were purified to homogeneity. The physicochemical parameters of the recombinant proteins were determined and compared with those of their natural placental counterparts. Except for a minor change in the pI, the proteins appeared to be indistinguishable by several criteria. Both recombinant PP4 and recombinant PP4-X were biologically active in a thromboplastin inhibition test and in a phospholipase A2 inhibition test.