A specific subunit of vitellogenin that mediates receptor binding

Abstract

Vitellogenin, an estrogen-induced serum protein synthesized in the liver, is composed of two Mr 250K polypeptides. It is specifically transported by a receptor-mediated endocytic process into the developing oocytes of virtually all oviparious animals. Following endocytosis, in the chicken, vitellogenin is specifically processed to yield several smaller products including the phosvitins (PV) and the lipovitellins (LV). These products are then stored within the oocyte until they are degraded during embryogenesis to provide nutrients for the developing embryo. Direct binding studies using iodinated vitellogenin demonstrate that vitellogenin binds to isolated oocyte membranes with a KD of 2.5 microM. Competition studies indicate that PV is a competitive inhibitor of vitellogenin binding. This leads us to propose that the PV portion of the circulating vitellogenin molecule mediates binding and uptake. Direct binding studies using iodinated PV show that PV binds to isolated oocyte membranes with a KD of 2.4 microM. Competition studies also demonstrate that 3.1 microM vitellogenin inhibits 50% of control 125I-PV binding, but IgG and bovine serum albumin at concentrations up to 10 microM have no effect on 125I-PV binding. Another series of competition experiments using a constant amount of vitellogenin and increasing amounts of 125I-PV indicate that vitellogenin acts as a competitive inhibitor of PV binding and has a KI of 2-3 microM. These results support our hypothesis that the receptor which mediates vitellogenin binding and uptake recognizes determinants on the PV portion of the native vitellogenin molecule.

Identification of vitellogenin receptors in the ovary of a teleost fish, the Mediterranean sea bass (Dicentrarchus labrax)

“…In the last decade, detailed information on the VTG receptors has been accumulated for birds, Gallu.s domesticus (Woods and Roth, 1984;Stifani et al, 1988Stifani et al, , 1990bBarber et al, 1991;Schneider, 1992;Shen et al, 1993;Bujo et al, 1994;Lachlan et al, 1994), amphibians, Xenopus laevis (Opresko and Wiley, 1987;Stifani et al, 1990b) and invertebrates (Rohrkasten and Ferenz, 1986;Hafer and Ferenz, 1991;Sappington et al, 1995 (Selman and Wallace, 1982).…”

Carbohydrate components of lipovitellin of the sand crab Emerita asiatica

“…In contrast to the invertebrate vitellogenin, vertebrate vitellogenin (phosvitin) is a sialoglycoprotein containing a single high-mannose N-linked oligosaccharide species (Shainkin and Perlmann, 1971a). Competition studies indicate that the phosvitin portion of vitellogenin molecule mediates the binding and uptake (Woods and Roth, 1984). However, no report is available on the oligosaccharide component of the crustacean vitellogenin/vitellin.…”

Affinity isolation and mass spectral analysis of 1,10-phenanthroline (OP)-stimulated UV-damaged-DNA binding proteins expressed in zebrafish (Danio rerio) embryos

“…Owing to its Zn-chelating activity, OP has been employed as a probe to determine the importance of Zn as a functional component of metalloproteins (Woods and Roth 1984;Wang and Jeng 2006). Identification of the 30-and 35-kDa polypeptides as homologs of the Lv1 domain of zfVg1 correlated well with the metal-dependent, UV-damaged-DNA binding activities of the two molecules (Lai et al 2006).…”

“…Analysis of UV damage DNA-binding activity in fractionated zebrafish extracts showed that proteins interacting preferentially with 6-4PPs were effectively separated from nonspecific binding proteins due to In oviparous vertebrates, Vgs are produced in the liver in response to estrogen stimulation. After secretion to the blood, these metalloproteins are taken up from the plasma by developing oocytes via receptormediated endocytosis and are cleaved into three portions-lipovitellin I (Lv1), phosvitin (PV), and lipovitellin II (Lv2) (Woods and Roth 1984;Montorzi et al 1995;Falchuk and Montorzi 2001). As a metalloprotein, the 220-kDa Vg of the frog Xenopus laevis was shown to carry different metals at varied levels.…”