A beta-1,3-glucan binding protein from the black tiger shrimp, Penaeus monodon

A beta-1,3-glucan binding protein (GBP) has been isolated from a shrimp hemocyte cDNA library. Its open reading frame consists of 1314 nucleotides with a polyadenylated sequence and a poly A tail. It encodes a polypeptide of 370 amino acids including a 17 amino acid-signal peptide. The mature protein has an estimated molecular mass of 39.5 kDa and a predicted pI of 5.5. Sequence comparison shows a high degree of similarity to invertebrate recognition proteins with glucanase-like domains for example, the lipopolysaccharide- and beta-1,3-glucan-binding protein (LGBP) from the freshwater crayfish, Pacifastacus leniusculus, coelomic cytolytic factor-1 from the earthworm, Eisenia foetida and the Gram negative bacteria binding protein from the mosquito, Anopheles gambiae as well as to sea urchin beta-1,3-glucanases and bacterial beta-1,3-glucanases or beta-1,3-, 1,4-glucanases. Northern blot analysis showed that the shrimp protein is constitutively expressed in hemocytes. Animals injected with curdlan or heat-killed bacterial cell of Vibrio harveyi, a shrimp pathogen, showed no significant change in the mRNA expression profile within 12h post-injection. After incubation of shrimp hemocyte lysate supernatant (HLS) with curdlan or zymosan, a protein with a molecular mass of 31 kDa was eluted from the incubated curdlan or zymosan, and, by immunoblotting, this 31-kDa band could be detected by an affinity-purified anti-crayfish LGBP antibody. In contrast, incubation of shrimp HLS with LPS showed no any reactive band detected on SDS-PAGE or by immunoblotting suggesting that the binding is specific for beta-1,3-glucan.