Novel Ca 2+ -independent C-type lectins, SPL-1 and SPL-2, were purified from the bivalve Saxidomus purpuratus. They are composed of dimers with either identical (SPL-2 composed of two B-chains) or distinct (SPL-1 composed of A-and B-chains) polypeptide chains, and show affinity for N-acetylglucosamine (GlcNAc)-and N-acetylgalactosamine (GalNAc)-containing carbohydrates, but not for glucose or galactose. A database search for sequence similarity suggested that they belong to the C-type lectin family. X-ray crystallographic analysis revealed definite structural similarities between their subunits and the carbohydrate-recognition domain (CRD) of the C-type lectin family. Nevertheless, these lectins (especially SPL-2) showed Ca 2+ -independent binding affinity for GlcNAc and GalNAc. The crystal structure of SPL-2/GalNAc complex revealed that bound GalNAc was mainly recognized via its acetamido group through stacking interactions with Tyr and His residues and hydrogen bonds with Asp and Asn residues, while widely known carbohydrate-recognition motifs among the C-type CRD (the QPD [Gln-Pro-Asp] and EPN [Glu-Pro-Asn] sequences) are not involved in the binding of the carbohydrate. Carbohydrate-binding specificities of individual A-and B-chains were examined by glycan array analysis using recombinant lectins produced from Escherichia coli cells, where both subunits preferably bound oligosaccharides having terminal GlcNAc or GalNAc with α-glycosidic linkages with slightly different specificities.
The C-type lectins SPL-1 and SPL-2 from the bivalve Saxidomus purpuratus are composed of A and B chains and of two B chains, respectively. They bind specific carbohydrates containing acetamido groups, such as N-acetylglucosamine (GlcNAc) and N-acetylgalactosamine (GalNAc), in a Ca 2+ -independent manner. Unlike ordinary C-type lectins, which require Ca 2+ ions for carbohydrate recognition, these lectins recognize specific carbohydrates mainly through interactions with the acetamido group without Ca 2+ ions, even though Ca 2+ enhances the binding affinity of these lectins, especially SPL-1. In the present study, the crystal structure of the SPL-1-GlcNAc complex in the presence of Ca 2+ revealed that the binding of SPL-1 to GlcNAc is stabilized by hydrogen bonds to the water molecule(s) coordinating Ca 2+ , whereas in ordinary C-type lectins Ca 2+ directly forms coordinate bonds to the hydroxy groups of carbohydrates. These differences may also allow SPL-1 and SPL-2 to recognize both GlcNAc and GalNAc, which have different orientations of the 4-hydroxy group. research communications Acta Cryst. (2020). F76, 271-277 Unno et al. Carbohydrate recognition by SPL-1 277
Toxascaris leonina was detected from 8 Japanese-breed domestic cats in Kanagawa Prefecture from October, 1983 to March, 1985. Feline infections had hardly been reported in Japan. Cat 1 had been kept indoor out of contact with imported or purebred cats. The ascarids of the cat seemed to be of the "dog strain", because of their high and low infectivity to dogs and cats, respectively. Cats 2-7 were kept together on the same farm and got in contact with imported cats. With ascarid eggs from one of those cats, dogs and cats were easily infected, so that the ascarids seemed to be of the "cat strain" which would have been introduced by imported cats and maintained on the farm. The history of Cat 8 was not determined, but its ascarids might be of the "cat strain" because of their high infectivity to both dogs and cats. Milbemycin D was administered orally to 3 and 2 naturally infected cats in doses of 0.05 and 0.1 mg/kg, respectively to deworm all the animals completely, except one administered with 0.05 mg/kg from which young adult worms were recovered at autopsy.
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