CRYSTAL-STRUCTURE OF TANDEM TYPE-III FIBRONECTIN DOMAINS FROM DROSOPHILA NEUROGLIAN AT 2.0 ANGSTROM

We report the crystal structure of two adjacent fibronectin type III r epeats from the Drosophila neural cell adhesion molecule neuroglian. E ach domain consists of two antiparallel beta sheets and is folded topo logically identically to single fibronectin type III domains from the extracellular matrix proteins tenascin and fibronectin. beta bulges an d left-handed polyproline II helices disrupt the regular beta sheet st ructure of both neuroglian domains. The hydrophobic interdomain interf ace includes a metal-binding site, presumably involved in stabilizing the relative orientation between domains and predicted by sequence com parision to be present in the vertebrate homolog molecule L1. The neur oglian domains are related by a near perfect 2-fold screw axis along t he longest molecular dimension. Using this relationship, a model for a rrays of tandem fibronectin type III repeats in neuroglian and other m olecules is proposed.