beta-1,3 glucanase

Function

In the animal kingdom, the known distribution of beta-1,3 glucanases is restricted to the eggs and digestive tract of echinoderms. The enzymes in these two cell types are of the same molecular weight and are antigenically similar. In the gut, the enzyme is presumed to catalyze the degradation of ingested algal beta-glucans.
Why beta-1,3 glucanase is in sea urchin eggs and is released at fertilization remains unclear. The enzyme is exocytosed from cortical granules 30 sec after fertilization, and active enzyme can be recovered from both young embryos and the perivitelline space surrounding the embryo. All but one of 13 species of sea urchin studied have beta-1,3 glucanase stored in cortical granules in unfertilized eggs. Nevertheless, its endogenous substrate and function are unknown (Bachman et al., 1996).

Protein

The start methionine of the deduced protein is followed by a hydrophobic stretch of 20 aa that is presumed to be the signal sequence. This stretch terminates with a glutamine, which is the presumed V8 protease cleavage site.
The mature protein is 499 aa, with a predicted Mr of 57 and pI of 4.1 (Bachman et al., 1996).

Subcellular location

The enzyme is exocytosed at fertilization and it persists in the perivitelline space until hatching (Bachman et al., 1996).

Expression Pattern

Nothern blot analysis recognized a message of 3.2 kb in eggs of L. variegatus and a slightly larger RNA was detected in the adult gut.
The beta-1,3 glucanase protein was followed during early sea urchin development by Western blot analysis using a polyclonal antibody made to the native enzyme. A single 68-kDa protein is present during early embryogenesis in L. variegatus. By 72 hr, the embryos are actively feeding and the enzyme reappears in the gut as revealed by immunofluorescence and by Western blot analyses (Bachman et al., 1996).

Protein level

Temporal accumulation
Method: Western blot analysis
Reference: Bachman et al., 1996

Stage Ovary Egg 2 cells Blastula Hatching blastula Mesenchyme blastula Gastrula Prism Pluteus 2 weeks

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