Characterization of vitellogenin and vitellin from land crab Potamon potamios: identification of a precursor polypeptide in the molecule.

A female-specific protein, vitellogenin (Vg), and its corresponding egg vitellin (Vn) were identified in the land crab Potamon potamios. Electrophoretic analysis of the hemolymph protein during the annual reproduction cycle revealed that the processing of vitellogenesis did not occur in males or in females of a previtellogenic stage. The analysis of ovarian and egg extracts revealed the presence of Vn, which was identical to Vg. Both Vg and Vn were present in three different aggregational states that represented monomeric, dimeric, and trimeric species of the proteins. In both proteins, the predominant form was the dimeric, which had a molecular mass of 551 kDa for Vg and 510 kDa for Vn. Under denaturing conditions, each of the individual Vg and Vn aggregates released three polypeptides with molecular masses of 115, 105, and 85 kDa. In spite of the difference in terms of native molecular mass, the Vg and Vn were similar in their lipid, carotenoid, and carbohydrate composition. However, Vg of some animals contained a fourth polypeptide with a molecular mass of 181 kDa. This polypeptide and the three other Vg and Vn polypeptides were immunoreactive against anti-Vg prepared from the 85 kDa Vg polypeptide. Furthermore, proteolytic cleavage experiments confirmed that the 115 and 105 kDa Vg polypeptides were derived from the 181 kDa polypeptide. We conclude that the presence of the 181 kDa polypeptide in the Vg molecule resulted in the higher molecular mass of Vg.