The JNK-interacting protein (JIP) group of scaffold proteins selectively mediates JNK-signaling by aggregating specific components of the MAPK cascade to form a functional JNK signaling module. May function as a regulator of vesicle transport, through interactions with the JNK-signaling components and motor proteins. Syd is required for efficient kinesin-I mediated axonal transport. Forms homo- and heterooligomeric complexes. Binds the TPR motif-containing C-terminal of kinesin light chain, Klc. Pre-assembled syd scaffolding complexes are then transported as a cargo of kinesin, to the required subcellular location. Partially edited. Target of Adar. Belongs to the JIP scaffold family. Truncated C-terminus. Intron retention.