Purification and characterization of alpha 2-macroglobulin from grass carp Ctenopharyngodon idellus: cloning a segment of the corresponding gene.

摘要

The plasma protein alpha 2-macroglobulin ( alpha 2M) was purified by gel filtration and anion-exchange chromatography from grass carp plasma. The alpha 2M consists of two different subunits of molecular weight 95 kDa and 80 kDa, respectively. The characteristics of grass carp alpha 2M are similar to mammalian alpha 2M, in that grass carp alpha 2M exists in two forms: a fast-form and a slow-form. The former is complexed with protease. The sequence of grass carp alpha 2M-conserved region and a region containing the bait region was determined by sequence analysis using polymerase chain reaction (PCR). The deduced amino acid sequence of the conserved region is similar to the alpha 2M sequence of common carp, however, the bait region amino acid sequence is dramatically distinct from that of common carp. This may partially explain the differential ability of alpha 2M of different species to inhibit different proteases. The alpha 2M was able to inhibit Aeromonas hydrophila extracellular protease (AhECPase) and thus may play a role in resistance to infection by this pathogen..