The major yolk protein in sea urchin egg yolk granules is a glycoprotein complex

Abstract

Major yolk protein (MYP) is the most abundant protein found in the yolk granules of sea urchin eggs. The structure of MYPs stored in the eggs of two sea urchin species from Strongylocentrotus intermedius and Mesocentrotus nudus were investigated. Egg-localized major yolk protein (EGMYP) extracted from the eggs of two species of sea urchins was assessed using disc-polyacrylamide gel electrophoresis and immunoelectrophoresis. The molecular weight of native EGMYP was 595 in S. intermedius eggs and 625 kDa in M. nudus eggs. The use of sodium dodecyl sulfate–polyacrylamide gel electrophoresis and Western blotting analysis under reducing conditions revealed that the EGMYP of S. intermedius separated into four bands (approximately 172, 116, 74 and 68 kDa), while the EGMYP of M. nudus resolved as a set of bands ranging from 175 to 58 kDa (approximately 175, 165, 153, 115, 102, 90, 78, 65 and 58 kDa). Yolk granules from eggs were isolated using sucrose density ultracentrifugation and examined using electron microscopy. The structures of purified EGMYP extracted from eggs and from yolk granules were similar in both species. The EGMYP stored in the eggs of the sea urchins was a glycoprotein complex, the protein structure of which, however, varied between the two species.