Mutational analysis of the L1 neuronal cell adhesion molecule identifies membrane-proximal amino acids of the cytoplasmic domain that are required for cytoskeletal anchorage.

The preferential localization of the L1 cell adhesion molecule in the axons and growth cones of differentiating neurons suggests the existence of a mechanism for targeting or anchoring the molecule to these locations. We have used B28 glioma cells, which have an extremely flattened morphology, as a model system to study the organization of L1 on the cell structure. Transfection of L1 cDNA into B28 cells results in expression of the L1 protein in organized linear cell surface arrays which are codistributed with cytoskeletal stress fibers, but not with microtubles or intermediate filaments. Transfection studies with L1 deletion mutants identify the juxtamembrane segment of the cytoplasmic domain as the critical entity for arrangement of L1 into ordered cell surface arrays. The seventh cytoplasmic amino acid of L1, lysine 1150, and to a lesser extent the fourth cytoplasmic amino acid, lysine 1147, appear to be critical residues for maintaining normal L1 anchorage and distribution.