Axonin-1 (N-terminal domain)
Gallus gallus (chicken)
Neurons are very unique for their enormously extended shape, with a long axon and branching dendrites connecting them through synapses to other cell. During neurogenesis the axons and dendrites grow out, find their right partners and form synapses with them to selectively generate a functional network. Neural cell adhesion molecules that are expressed by neurons play an important role in this axon growth and guidance. Axonin-1/TAG-1, a neural cell adhesion molecule is a member of the immunoglobulin superfamily.
It consists of six immunoglobulin (Ig) domains followed by four fibronectin type III domains anchored to the membrane by glycosylphosphatidylinositol. Axonin-1/TAG-1 mediates cell-cell contacts through homophilic and heterophilic interactions. The crystal structure of the ligand binding fragment of axonin-1/TAG-1 composed of the four N-terminal Ig domains is reported here. The overall structure of axonin-1Ig1-4 is a U-shaped arrangement due to contacts between domains 1 and 4 and 2 and 3, resulting in the formation of a compact module. In the crystal, axonin-1Ig1-4 molecules are aligned in a string with adjacent molecules oriented in anti-parallel fashion. This arrangement and mutagenesis analysis based on the structure suggest that cell adhesion by homophilic axonin-1 interaction occurs by the formation of a linear zipper-like array in which the axonin-1 molecules are alternately provided by the two apposed membranes.
Protein Data Bank (PDB)
Freigang, J. Proba, K. Leder, L. Diederichs, K. Sonderegger, P. Welte, W.; "The crystal structure of the ligand binding module of axonin-1/TAG-1 suggests a zipper mechanism for neural cell adhesion."; Cell; (2000) 101:425-433 PubMed:10830169.
author: Aki Nagata