Determination of the minimum carbohydrate-recognition domain in two C-type animal lectins.

Comparison of the primary structures of numerous Ca(2+)-dependent animal lectins reveals the presence of a common sequence motif which has been suggested to form the carbohydrate-recognition domain in these proteins. The extent of the functional carbohydrate-recognition domains in two rat C-type lectins, mannose-binding protein A and the major subunit of the asialoglycoprotein receptor (rat hepatic lectin 1), has been defined by expressing truncated fragments of the proteins in an in vitro transcription and translation system. The shortest fully functional fragments constitute the COOH-terminal 120 amino acids of mannose-binding protein A and 135 amino acids of rat hepatic lectin 1. These segments correspond closely to protease-resistant protein cores which can be isolated from the native lectins. The NH2-terminal boundary of each minimum carbohydrate-recognition domain falls near the site of an intron in the corresponding gene.