Identification of Major Proteins of a Very Stable High Molecular Mass Multi-Protein Complex of Human Placental Tissue Possessing Nine Different Catalytic Activities

Abstract

Human placenta is an organ protecting, feeding, and regulating the grooving of the embryo. Therefore, identification and characterization of placental components including proteins and their multi-protein complexes is an important step to understanding the placenta function. Here we analyzed for the first time human placentas extremely stable multi-protein complex (SPC, ~1000 kDa) by MALDI MS and MS/MS spectrometry using proteins tryptic hydrolyzates after proteins separation by SDS-PAGE and 2-D electrophoresis. The formation of such a very stable complex due to the random association of several various proteins is very unlikely. It was shown that SPCs contain twelve proteins: hemoglobin, alkaline phosphatase, cytoplasmic actin, human serum albumin, chorionic somatomammotropin hormone, heat shock protein beta-1, peroxiredoxin-1, 78 kDa glucose-regulated protein, protein disulfide isomerase A3, serotransferrin, annexin A5, and IgGs. These twelve proteins have in themselves many different and important biological functions, which can be inherent for these proteins in the complex. In addition, the complex demonstrated nine different enzymatic activities: DNase, RNase, ATPase, phosphatase, protease, amylase, catalase, peroxidase (H2O2-dependent) and oxidoreductase (H2O2-independent). The efficiency of the catalysis of each of these reactions by SPC preparations from three placentas was comparable. It was shown that hydrolysis of r(pU)23, r(pA)23, and r(pC)23 leads to the formation of 1-22-mer oligonucleotides, while digestion of microRNA mirR137 is a site-specific (3A-4U > 9U-10A > 8U-9U ≥ 15U-16A) resulting in the formation of only four major products. A large number of potentially possible functions of the complex in accordance with the functions of its individual proteins are considered. Progress in the study of placental proteins complexes can promote understanding of their biological functions.