Mutations of the two conserved potential N-linked glycosylation sites and of one of the amino acids (R64) involved in the formation of a salt bridge rendered a protein with no activity. The introduced mutations very likely resulted in major conformational changes in the protein. Preliminary data from our laboratory indicates that enzymatic removal of N-linked carbohydrates with peptide-N-glycosidase F results in a significant reduction of the activity of the protein. In addition, we have previously established that N-linked glycosylation is required for interaction of murine PSG17 with CD9 [65] . It remains to be determined whether the removal of the carbohydrates just in the N-domain is enough to destroy the activity of the protein.