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Open Access Research article

The structure of the Ca2+-binding, glycosylated F-spondin domain of F-spondin - A C2-domain variant in an extracellular matrix protein

Kemin Tan1 and Jack Lawler2

Author Affiliations

1 Midwest Center for Structural Genomics and Structural Biology Center, Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA

2 Division of Experimental Pathology, Department of Pathology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02215, USA

BMC Structural Biology 2011, 11:22  doi:10.1186/1472-6807-11-22

Published: 10 May 2011

Abstract

Background

F-spondin is a multi-domain extracellular matrix (ECM) protein and a contact-repellent molecule that directs axon outgrowth and cell migration during development. The reelin_N domain and the F-spondin domain (FS domain) comprise a proteolytic fragment that interacts with the cell membrane and guides the projection of commissural axons to floor plate. The FS domain is found in F-spondins, mindins, M-spondin and amphiF-spondin.

Results

We present the crystal structure of human F-spondin FS domain at 1.95Å resolution. The structure reveals a Ca2+-binding C2 domain variant with an 8-stranded antiparallel β-sandwich fold. Though the primary sequences of the FS domains of F-spondin and mindin are less than 36% identical, their overall structures are very similar. The unique feature of F-spondin FS domain is the presence of three disulfide bonds associated with the N- and C-termini of the domain and a highly conserved N-linked glycosylation site. The integrin-binding motif found in mindin is not conserved in the F-spondin FS domain.

Conclusion

The structure of the F-spondin FS domain completes the structural studies of the multiple-domain ECM molecule. The homology of its core structure to a common Ca2+- and lipid-binding C2 domain suggests that the F-spondin FS domain may be responsible for part of the membrane targeting of F-spondin in its regulation of axon development. The structural properties of the FS domain revealed in this study pave the way for further exploration into the functions of F-spondin.