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

Tan K, Lawler J - BMC Struct. Biol. (2011)

Bottom Line: The FS domain is found in F-spondins, mindins, M-spondin and amphiF-spondin.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Midwest Center for Structural Genomics and Structural Biology Center, Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA. ktan@anl.gov

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.

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The structural alignment of F-spondin with mindin and a typical C2 domain. (A) An alignment of FS domains of F-spondin (in cyan) and mindin (in red). Ca atoms are shown as spheres. The integrin-binding LEV triplet of human mindin is drawn in stick format. Only the C-terminal β8 stand is labeled. (B) An alignment of the FS domain of F-spondin (in cyan) with the N-terminal Ca-dependent lipid-binding/C2 domain of cytosolic phospholipase A2 (in magenta, PDB code:1CJY)[27].
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Figure 5: The structural alignment of F-spondin with mindin and a typical C2 domain. (A) An alignment of FS domains of F-spondin (in cyan) and mindin (in red). Ca atoms are shown as spheres. The integrin-binding LEV triplet of human mindin is drawn in stick format. Only the C-terminal β8 stand is labeled. (B) An alignment of the FS domain of F-spondin (in cyan) with the N-terminal Ca-dependent lipid-binding/C2 domain of cytosolic phospholipase A2 (in magenta, PDB code:1CJY)[27].

Mentions: The C-terminal region of FS domains is one of the most diversified regions in the amino acid sequences (Figure 4). The location of the C-terminus of F-spondin or mindin is different according to the structures of their FS domains. In the construct of mindin[16], the C-terminus was truncated at R223, which is equivalent to E413 of F-spondin. In the structure reported here, E413 is before C415 and on the structured C-terminal loop between the β8 and the β8' strands. In mindin, there is no disulfide bond tethering its C-terminal region to its N-terminus. The end of the β8 strand is L218 and the following residue R219 starts to peel off from the mindin FS domain (Figure 5A), resulting in disordering of most of the other C-terminal residues of the construct[16]. In F-spondin, residue A409, the equivalent of R219 in mindin, is the third residue from the end of the β8 strand (Figure 4). The C-terminal loop region observed in F-spondin seemingly extends the C-termini of the FS domain to at least V426 (Figure 2). We note that exon 10 of human F-spondin genomic DNA encodes the C-terminal region of the FS domain, from G412 to E436. It is possible that the C-terminus of F-spondin FS domain extends much beyond the disulfide bond formed by C415. However, we can't exclude the possibility that the C-terminal structured region (from N416 to V426) results from molecular packing in the crystal.


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

Tan K, Lawler J - BMC Struct. Biol. (2011)

The structural alignment of F-spondin with mindin and a typical C2 domain. (A) An alignment of FS domains of F-spondin (in cyan) and mindin (in red). Ca atoms are shown as spheres. The integrin-binding LEV triplet of human mindin is drawn in stick format. Only the C-terminal β8 stand is labeled. (B) An alignment of the FS domain of F-spondin (in cyan) with the N-terminal Ca-dependent lipid-binding/C2 domain of cytosolic phospholipase A2 (in magenta, PDB code:1CJY)[27].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3117680&req=5

Figure 5: The structural alignment of F-spondin with mindin and a typical C2 domain. (A) An alignment of FS domains of F-spondin (in cyan) and mindin (in red). Ca atoms are shown as spheres. The integrin-binding LEV triplet of human mindin is drawn in stick format. Only the C-terminal β8 stand is labeled. (B) An alignment of the FS domain of F-spondin (in cyan) with the N-terminal Ca-dependent lipid-binding/C2 domain of cytosolic phospholipase A2 (in magenta, PDB code:1CJY)[27].
Mentions: The C-terminal region of FS domains is one of the most diversified regions in the amino acid sequences (Figure 4). The location of the C-terminus of F-spondin or mindin is different according to the structures of their FS domains. In the construct of mindin[16], the C-terminus was truncated at R223, which is equivalent to E413 of F-spondin. In the structure reported here, E413 is before C415 and on the structured C-terminal loop between the β8 and the β8' strands. In mindin, there is no disulfide bond tethering its C-terminal region to its N-terminus. The end of the β8 strand is L218 and the following residue R219 starts to peel off from the mindin FS domain (Figure 5A), resulting in disordering of most of the other C-terminal residues of the construct[16]. In F-spondin, residue A409, the equivalent of R219 in mindin, is the third residue from the end of the β8 strand (Figure 4). The C-terminal loop region observed in F-spondin seemingly extends the C-termini of the FS domain to at least V426 (Figure 2). We note that exon 10 of human F-spondin genomic DNA encodes the C-terminal region of the FS domain, from G412 to E436. It is possible that the C-terminus of F-spondin FS domain extends much beyond the disulfide bond formed by C415. However, we can't exclude the possibility that the C-terminal structured region (from N416 to V426) results from molecular packing in the crystal.

Bottom Line: The FS domain is found in F-spondins, mindins, M-spondin and amphiF-spondin.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Midwest Center for Structural Genomics and Structural Biology Center, Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA. ktan@anl.gov

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.

Show MeSH