Solution structures of the first and fourth TSR domains of F-spondin.

F-spondin is a protein mainly associated with neuronal development. It attaches to the extracellular matrix and acts in the axon guidance of the developing nervous system. F-spondin consists of eight domains, six of which are TSR domains. The TSR domain family binds a wide range of targets. Here we present the NMR solution structures of TSR1 and TSR4. TSR domains have an unusual fold that is characterized by a long, nonglobular shape, consisting of two beta-strands and one irregular extended strand. Three disulfide bridges and stack of alternating tryptophan and arginine side-chains stabilize the structure. TSR1 and TSR4 structures are similar to each other and to the previously determined TSR domain X-ray structures from another protein, TSP, although TSR4 exhibits a mobile loop not seen in other structures.