| Summary: | Bovine conglutinin is a member of the collectin family of innate immune system proteins. Crystals of the native protein have been grown and X-ray diffraction data collected. The space group is tetragonal P4) with one CRD per asymmetric unit. The crystallographic structure of a recombinant bovine conglutinin carbohydrate recognition domain (CRD) has been solved to 1.2SA in native and 1.46A in ligand-bound form. The native structure has been solved by molecular replacement with the coordinates of oneCRD of human trimeric surfactant protein-D (hSP-D) as the search" model. hSP-D is the closest molecule to conglutinin phylogenetically for which the crystallographic structure is known. The fold is demonstrated to be the same as the highly conserved C-type lectin fold found in coUectins. The ligand bound structure was solved by soaking N-acetylglucosamine, the highest affmity ligand, into native crystals. Binding is shown to be by vicinal equatorial hydroxyl groups on the sugar ring of the ligand, confirming the carbohydrate recognition previously demonstrated for hSP-D and rat mannose binding proteins A and C. An additional hydrogen bond is observed between the acetyl group of the ligand and a protein lysine residue which could account for the high affinity of conglutinin for this ligand. The fmal R-factors are Rc:onv 21.7, Rrn,., 24.3 for the native, and ~v 20.3, Rne 22.3 for the ligand-bound structure. Attempts were made to grow crystals of a trimeric conglutinin fragment consisting of the a-helical coiled-coil neck region and three eROs. The crystals grown did not diffract to high enough resolution to allow data collection and structure solution. Reports that N-acetylmuramic acid, a component of bacterial cell wall peptidoglycan, was a high affinity ligand for hSP-D were followed up. Cocrystailisation trials failed to grow diffraction quality crystals.
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