THE SEA-URCHIN EGG JELLY COAT CONSISTS OF GLOBULAR GLYCOPROTEINS BOUND TO A FIBROUS FUCAN SUPERSTRUCTURE

Intact egg jelly (EJ) coats surrounding eggs of the sea urchin Strongy locentrotus purpuratus were visualized in stereo images of platinum re plicas produced by the quick-freeze, deep-etch, rotary-shadowing techn ique. The hydrated EJ coat forms an extensive fibrous network that mak es contact with the vitelline layer at the egg surface. Fibers are dec orated along their length with particles, particle density being highe st in the interior regions of the coat. The macromolecular components making up the EJ network were visualized by rotary-shadowing of mica-a dsorbed EJ samples. Whole EJ coats solubilized in pH 5 seawater and sp read on the mica surface consist of complex networks of branching fibe rs decorated with large patches of amorphous material. As we have prev iously shown (Keller and Vacquier, 1994), EJ boiled in a dissolution b uffer containing SDS and beta-mercaptoethanol and applied to a Sephacr yl-500 gel filtration column can be separated into three fractions: a 380-kDa fucose sulfate polymer (FSP), which elutes in the void volume, and two column-included fractions consisting of intermediate (300 kDa ) and low-molecular-weight (30- to 138-kDa) glycoproteins. Rotary-shad owing of the FSP fraction reveals branched fibrous components similar in appearance to that of solubilized whole EJ but devoid of any partic ulate decoration. In contrast, intermediate- and low-molecular-weight EJ components are strictly globular in appearance but are distinguisha ble on the basis of size. Ion-exchange purification of whole EJ yields two glycoproteins, of 82 and 138 kDa, having AR-inducing activity (Ke ller and Vacquier, 1994). Platinum replication shows these active comp onents to be small spherical molecules about 8 nm in diameter. The abo ve fractionation scheme requires harsh dissociation conditions. Indeed , if EJ is not boiled in SDS buffer before fractionation, the 300-kDa fraction and the FSP appear together in the void volume. Rotary-shadow ing of this complex reveals a multistranded polymer, decorated with gl ycoproteins at specific kink points. Taken together, our data suggest that the EJ network is composed of a fucose sulfate polymer superstruc ture to which glycoproteins are bound. (C) 1994 Academic Press, Inc.