Carbohydrate Specificity of the Oyster (Crassostrea virginica) Galectin CvGal: Recombinant Expression and Characterization of Selected Carbohydrate Recognition Domains

It is widely accepted that recognition of exposed glycans on the cell surface of potential pathogens by host humoral or cell-associated lectins is a key component of the innate immune response of vertebrates and invertebrates. However, the protozoan parasite Perkinsus marinus causes “Dermo” disease in the eastern oyster Crassostrea virginica, and is responsible for catastrophic damage to shellfisheries in North America. Until recently, the parasite's mechanism(s) for entry into the hemocyte had remained obscure. The recent results suggest identification and characterization in oyster hemocytes a galectin (CvGal) with a unique carbohydrate-recognition domain (CRD) organization that, unlike most mammalian galectins, recognizes exogenous carbohydrate ligands [1]. CvGal binds to a variety of potential microbial pathogens, phytoplankton components, and Perkinus trophozoites, suggesting that it functions as a hemocyte surface receptor for this parasite, and facilitates its entry into the host cells. Unlike all galectins known so far, CvGal displays four CRDs that contain seven of the nine amino acid residues that bind ligand in the bovine galectin-1. Because the CvGal CRDs are similar, but not identical to each other, their carbohydrate specificities may be also different. To characterize their carbohydrate specificity, we initiated the recombinant expression of the CvGal CRDs, individually and as combinations of 2 and 3 CRDs to enable the rigorous analysis of their binding specificity and affinity. We developed expression constructs into a pET expression vector for all four individual CRDs, as well as CRDs 2-3 and CRDs1-2-3. Expression, purification, and characterization of each recombinant CRD are underway. Acknowledgements: Thanks go to the Center of Marine Biotechnology, University of Maryland, and to Dr. Geraldo Vasta and Dr. Rifts Ahmed, and Tyson Wendland. (Supported by NSF Grant IOS-0822257 and NIH Grant RO1 GM070589-01 to G.R.V Reference: [1] Tasumi S, Vasta GR, (2007), J Immunol, 179: 3086–3098.