May play a role in vesicle trafficking. H2O + NAD(+) = ADP-D-ribose + H(+) + nicotinamide A number of isoforms are produced. According to EST sequences. The TIR domain mediates NAD(+) hydrolase (NADase) activity. Self-association of TIR domains is required for NADase activity. Belongs to the VAMP-associated protein (VAP) (TC 9.B.17) family.