PDBsum entry: 2p6a

Signaling protein

PDB id: 2p6a

Contents

Protein chains

116 a.a. *

292 a.a. *

Ligands

ALA-ALA-ALA-ALA-ALA-ALA-ALA-ALA-ALA-ALA

* Residue conservation analysis

PDB id:

2p6a

Name:

Signaling protein

Title:

The structure of the activin:follistatin 315 complex

Structure:

Inhibin beta a chain. Chain: a, b. Synonym: activin beta-a chain, erythroid differentiation pr edf. Engineered: yes. Follistatin. Chain: d, c. Synonym: fs, activin-binding protein. Engineered: yes.

Source:

Homo sapiens. Human. Organism_taxid: 9606. Gene: inhba. Expressed in: cricetulus griseus. Expression_system_taxid: 10029. Gene: fst.

Resolution:

3.40Å R-factor: 0.225 R-free: 0.324

Authors:

T.F.Lerch,S.Shimasaki,T.K.Woodruff,T.S.Jardetzky

Key ref:

T.F.Lerch et al. (2007). Structural and biophysical coupling of heparin and activin binding to follistatin isoform functions. J Biol Chem, 282, 15930-15939. PubMed id: 17409095 DOI: 10.1074/jbc.M700737200

Date:

16-Mar-07 Release date: 03-Apr-07

Protein chains

P08476  (INHBA_HUMAN) -  Inhibin beta A chain

Seq: 426 a.a.

Struc: 116 a.a.

Protein chains

P19883  (FST_HUMAN) -  Follistatin

Seq: 344 a.a.

Struc: 292 a.a.

 Gene Ontology (GO) functional annotation 

• Cellular component: extracellular region (3 terms)
• Biological process: gamete generation (14 terms)
• Biochemical function: signal transducer activity (5 terms)

DOI no: 10.1074/jbc.M700737200

J Biol Chem 282:15930-15939 (2007)

PubMed id: 17409095

Structural and biophysical coupling of heparin and activin binding to follistatin isoform functions.

T.F.Lerch, S.Shimasaki, T.K.Woodruff, T.S.Jardetzky.

ABSTRACT

Follistatin (FS) regulates transforming growth factor-beta superfamily ligands and is necessary for normal embryonic and ovarian follicle development. Follistatin is expressed as two splice variants (FS288 and FS315). Previous studies indicated differences in heparin binding between FS288 and FS315, potentially influencing the physiological functions and locations of these isoforms. We have determined the structure of the FS315-activin A complex and quantitatively compared heparin binding by the two isoforms. The FS315 complex structure shows that both isoforms inhibit activin similarly, but FS315 exhibits movements within follistatin domain 3 (FSD3) apparently linked to binding of the C-terminal extension. Surprisingly, the binding affinities of FS288 and FS315 for heparin are similar at lower ionic strengths with FS315 binding decreasing more sharply as a function of salt concentration. When bound to activin, FS315 binds heparin similarly to the FS288 isoform, consistent with the structure of the complex, in which the acidic residues of the C-terminal extension cannot interact with the heparin-binding site. Activin-induced binding of heparin is unique to the FS315 isoform and may stimulate clearance of FS315 complexes.

Selected figure(s)

Figure 2.
FIGURE 2. The structure of the activin-follistatin 315 complex. Shown from the top (A) and side (B). Activin monomers are shaded in blue. One follistatin molecule is in green, while the other is in red, and the shading darkens from the N to C termini. Similar to the activin-FS288 structure, two binding sites are made on activin by each follistatin. Site 1 is made by the ND contacting the concave fingers of one activin monomer and the helical wrist region of the other, while site 2 is composed of the kazal region of FSD1 and the entire FSD2 of follistatin contacting the "knuckle" region on a single activin monomer. C, continuous density (blue) was only observed for a portion of the C-terminal extension (red) on either follistatin molecule. On one (left), residues 289-299 were built, revealing the direction of the C terminus of FS315. The C terminus threads a gap between FSD2 and FSD3 as it extends inwards, toward activin. On the other follistatin molecule (right) the density shown permitted the building of a 10-residue fragment, but side chains could not be unambiguously modeled, preventing identification of this region within the C-terminal extension. This fragment also lies between FSD2 and FSD3 and likely corresponds to residues 295-304, based on symmetry with the first follistatin molecule.

Figure 4.
FIGURE 4. Structural implications for heparin binding. A, the sequence of the acidic C terminus, unique to FS315. The distance from follistatin residue 299 (the last residue observed in this structure) to the end of the acidic stretch is 19 Å if in an extended conformation. Measurement from residues 295-299 (red), the beginning of the acidic tail, to the HBS (blue) shows that this acidic portion of the C terminus is incapable of directly competing for heparin binding (B). This is also true for competition across the complex (C) where the C terminus is somewhat closer to the HBS of the adjacent molecule (shown in green), but would still be unable to place the negatively charged C-terminal residues near the positively charged HBS. This structural observation suggests that FS315 may associate with heparin differently in its free and activin-bound states.

The above figures are reprinted by permission from the ASBMB: J Biol Chem (2007, 282, 15930-15939) copyright 2007.

Figures were selected by the author.