PDBsum entry 1lr9

Hormone/growth factor

PDB id: 1lr9

Contents

Protein chain

73 a.a. *

Waters ×28

* Residue conservation analysis

References listed in PDB file

Key reference

Title

Crystal structures of the heparan sulfate-Binding domain of follistatin. Insights into ligand binding.

Authors

C.A.Innis, M.Hyvönen.

Ref.

J Biol Chem, 2003, 278, 39969-39977. [DOI no: 10.1074/jbc.M211284200]

PubMed id

12867435

Abstract

Follistatin associates with transforming growth factor-beta-like growth factors such as activin or bone morphogenetic proteins to form an inactive complex, thereby regulating processes as diverse as embryonic development and cell secretion. Although an interaction between heparan sulfate chains present at the cell surface and follistatin has been recorded, the impact of this binding reaction on the follistatin-mediated inhibition of transforming growth factor-beta-like signaling remains unclear. To gain a structural insight into this interaction, we have solved the crystal structure of the presumed heparan sulfate-binding domain of follistatin, both alone and in complex with the small heparin analogs sucrose octasulfate and D-myo-inositol hexasulfate. In addition, we have confirmed the binding of the sucrose octasulfate and D-myo-inositol hexasulfate molecules to this follistatin domain and determined the association constants and stoichiometries of both interactions in solution using isothermal titration calorimetry. Overall, our results shed light upon the structure of this follistatin domain and reveal a novel conformation for a hinge region connecting epidermal growth factor-like and Kazal-like subdomains compared with the follistatin-like domain found in the extracellular matrix protein BM-40. Moreover, the crystallographic analysis of the two protein-ligand complexes mentioned above leads us to propose a potential location for the heparan sulfate-binding site on the surface of follistatin and to suggest the involvement of residues Asn80 and Arg86 in such a follistatin-heparin interaction.

Figure 2.
FIG. 2. Fs1 structure. Left, ribbon diagram of the Fs1/SOS structure, highlighting secondary structure elements. Right, diagrams of the superimposed C[ ]traces for the Fs1 (red), Fs1/SOS (yellow), and Fs1/Ins6S (blue) structures; the loop involved in crystal contacts is circled, and the SOS and Ins6S are shown in stick representation. In both halves of this figure, disulfide bonds are depicted in white with red numbering, and secondary structure elements are labeled in dark blue. This figure and the following three-dimensional representations of molecules were generated using the program Molscript (50) and rendered with Raster3D (51).

Figure 5.
FIG. 5. Interactions between SOS/Ins6S and Fs1. A and B, binding of SOS (A) and Ins6S (B) to Fs1. Sulfate groups from these two heparin analogs are numbered, along with protein residues involved in the interaction. C, superimposition of the Fs1/SOS (ochre) and Fs1/Ins6S (blue) structures, showing the relative positioning of sulfate groups in the binding site. D-F, the interfaces between the heparin-binding region of one Fs1 molecule (blue) and the Kazal-like subdomain of one of its symmetry-related counterparts (ochre) are depicted for each of the three Fs1 structures. Residues involved in protein-protein and additional protein-ligand contacts are labeled, as are the sulfate groups interacting with the symmetry-related Fs1 molecules.

The above figures are reprinted by permission from the ASBMB: J Biol Chem (2003, 278, 39969-39977) copyright 2003.