STRUCTURAL REQUIREMENTS FOR ASSOCIATION OF NEUROFASCIN WITH ANKYRIN

This paper presents the first structural analysis of the cytoplasmic d omain of neurofascin, which is highly conserved among the L1CAM family of cell adhesion molecules, and describes sequence requirements for n eurofascin-ankyrin interactions in living cells. The cytoplasmic domai n of neurofascin dimerizes in solution, has an asymmetric shape, and e xhibits a reversible temperature-dependent beta-structure. Residues Se r(56)-Tyr(81) are necessary for ankyrin binding but do not contribute to either dimerization or formation of structure. Transfected neurofas cin recruits GFP-tagged 270-kDa ankyrin, to the plasma membrane of hum an embryo kidney 293 cells. Deletion mutants demonstrate that the sequ ence Ser(56)-Tyr(81) contains the major ankyrin-recruiting activity of neurofascin, Mutations of the FIGQY tyrosine (Y81H/A/E) greatly impai r neurofascin-ankyrin interactions. Mutation of human L1 at the equiva lent tyrosine (Y1229H) is responsible for certain cases of mental reta rdation (Van Camp, G,, Fransen, E., Vits, L,, Raes, G,, and Willems, P , J, (1996) Hum. Mutat. 8, 391). Mutations F77A and E73Q greatly impai r ankyrin binding activity, whereas mutation D74N and a triple mutatio n of D57N/D58N/D62N result in less loss of ankyrin binding activity. T hese results provide evidence for a highly specific interaction betwee n ankyrin and neurofascin and suggest that ankyrin association with L1 is required for L1 function in humans.