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Characterization of an Î±âmacroglobulinâlike glycoprotein isolated from the plasma of the soft tick Ornithodoros moubata
- KopÃ¡Äek, Petr, Weise, Christoph, Saravanan, Thangamani, VÃtovÃ¡, KateÅina, Grubhoffer, Libor
- European journal of biochemistry 2000 v.267 no.2 pp. 465-475
- Ornithodoros moubata, active sites, amino acid sequences, cattle, glycoproteins, methylamine, molecular weight, polyacrylamide gel electrophoresis, polymerase chain reaction, polypeptides, pretreatment, sequence analysis, soybeans, ticks, trypsin, trypsin inhibitors
- We report the identification of the first representative of the Î±â2âmacroglobulin family identified in terrestrial invertebrates. An abundant acidic glycoprotein was isolated from the plasma of the soft tick Ornithodoros moubata. Its molecular mass is about 420âkDa in the native state, whereas in SDS/PAGE it migrates as one band of 190âkDa under nonreducing conditions and a band of 92âkDa when reduced. Chemical deglycosylation reveals that it is composed of two different subunits, designated A and B. The Nâterminal aminoâacid sequence of subunitâA is similar to the Nâterminus of invertebrate Î±â2âmacroglobulin. Sequence analysis of several internal peptides confirms that the tick protein belongs to the Î±â2âmacroglobulin family, and the protein is therefore referred to as tick Î±âmacroglobulin (TAM). Functional analyses strengthen this assignment. TAM inhibits trypsin and thermolysin cleavage of the highâmolecularâweight substrate azocoll in a manner similar to that of bovine Î±â2âmacroglobulin. This effect is abolished by preâtreatment of TAM with methylamine. In the presence of TAM, trypsin is protected against activeâsite inhibition by soybean trypsin inhibitor. We cloned and sequenced a PCR product containing sequences from both subunits and spanning the Nâterminus of subunitâB and the putative âbait regionâ (a segment of Î±â2âmacroglobulin which serves as target for various proteases). This indicates that the two subunits are generated from a precursor polypeptide by postâtranslational processing.