PDBsum entry 2o9v

Signaling protein/cell adhesion

PDB id: 2o9v

Contents

Protein chain

67 a.a. *

Ligands

VAL-PRO-PRO-PRO-VAL-PRO-PRO-PRO-PRO-SER

Waters ×97

* Residue conservation analysis

PDB id:

2o9v

Name:

Signaling protein/cell adhesion

Title:

The second sh3 domain from ponsin in complex with the paxillin proline rich region

Structure:

Ponsin. Chain: a. Fragment: src homology 3 (sh3) domain. Engineered: yes. Paxillin. Chain: b. Fragment: proline rich region. Engineered: yes

Source:

Homo sapiens. Human. Organism_taxid: 9606. Gene: sorbs1. Expressed in: escherichia coli. Expression_system_taxid: 562. Synthetic: yes. Other_details: the peptide was chemically synthesized. The sequence of the peptide is naturally found in homo sapiens (human)

Resolution:

1.63Å R-factor: 0.144 R-free: 0.177

Authors:

N.Pinotsis,M.Wilmanns

Key ref:

K.Gehmlich et al. (2007). Paxillin and ponsin interact in nascent costameres of muscle cells. J Mol Biol, 369, 665-682. PubMed id: 17462669 DOI: 10.1016/j.jmb.2007.03.050

Date:

14-Dec-06 Release date: 30-Oct-07

Protein chain

Q9BX66  (SRBS1_HUMAN) -  Sorbin and SH3 domain-containing protein 1 from Homo sapiens

Seq: 1292 a.a.

Struc: 67 a.a.*

* PDB and UniProt seqs differ at 6 residue positions (black crosses)

Enzyme reactions

• Enzyme class: E.C.?

DOI no: 10.1016/j.jmb.2007.03.050

J Mol Biol 369:665-682 (2007)

PubMed id: 17462669

Paxillin and ponsin interact in nascent costameres of muscle cells.

K.Gehmlich, N.Pinotsis, K.Hayess, P.F.van der Ven, H.Milting, A.El Banayosy, R.Körfer, M.Wilmanns, E.Ehler, D.O.Fürst.

ABSTRACT

Muscle differentiation requires the transition from motile myoblasts to sessile myotubes and the assembly of a highly regular contractile apparatus. This striking cytoskeletal remodelling is coordinated with a transformation of focal adhesion-like cell-matrix contacts into costameres. To assess mechanisms underlying this differentiation process, we searched for muscle specific-binding partners of paxillin. We identified an interaction of paxillin with the vinexin adaptor protein family member ponsin in nascent costameres during muscle differentiation, which is mediated by an interaction of the second src homology domain 3 (SH3) domain of ponsin with the proline-rich region of paxillin. To understand the molecular basis of this interaction, we determined the structure of this SH3 domain at 0.83 A resolution, as well as its complex with the paxillin binding peptide at 1.63 A resolution. Upon binding, the paxillin peptide adopts a polyproline-II helix conformation in the complex. Contrary to the charged SH3 binding interface, the peptide contains only non-polar residues and for the first time such an interaction was observed structurally in SH3 domains. Fluorescence titration confirmed the ponsin/paxillin interaction, characterising it further by a weak binding affinity. Transfection experiments revealed further characteristics of ponsin functions in muscle cells: All three SH3 domains in the C terminus of ponsin appeared to synergise in targeting the protein to force-transducing structures. The overexpression of ponsin resulted in altered muscle cell-matrix contact morphology, suggesting its involvement in the establishment of mature costameres. Further evidence for the role of ponsin in the maintenance of mature mechanotransduction sites in cardiomyocytes comes from the observation that ponsin expression was down-regulated in end-stage failing hearts, and that this effect was reverted upon mechanical unloading. These results provide new insights in how low affinity protein-protein interactions may contribute to a fine tuning of cytoskeletal remodelling processes during muscle differentiation and in adult cardiomyocytes.

Selected figure(s)

Figure 3.
Figure 3. The structure of the ponsin SH3.2 domain in complex with the paxillin PRR motif (SH3.2/paxillin PRR). (a) Overall fold of the complex. The SH3 domain is shown in light blue ribbon representation with the main residues of the interface shown as sticks. The two main SH3 loops (RT and n-Src) are also indicated. The paxillin polypeptide is depicted in orange sticks. The orientation of the peptide is indicated by labeling key residue positions (P[2], P[0], P[− 2]). (b) Electrostatic potential representation of the SH3 domain in the same orientation as shown in (a). The first hydrophobic loop is shown on the left, while the third groove is flanked by two negatively charged areas. The weighted (2F[o]–F[c]) electron density map of the peptide computed with phases of the final model is also shown. (c) 2D representation of the ponsin/paxillin interaction. The panel was generated using LIGPLOT.^65 (d) Stick representation of the main residues from ponsin (in yellow) and paxillin (in orange) that participate in the binding interface. (e) The specific conformations of the Asp835 and Glu839 for the non-bound (cyan, two different conformations) and bound (light blue) paxillin peptide in the RT loop. (f) Multiple sequence alignment of the three SH3 domains of ponsin. The positions of the secondary structural elements including the RT and n-Src loops are indicated, as determined in the two crystal structures of the SH3.2 domain. Residues involved in the binding interface with the paxillin PRR peptide are shown in black boxes. Residues in blue colour are conserved in two of the three domains and additionally represented in lower case in the consensus line. Residues that are similar are shown in red and additionally capital letters in the consensus line (including also: ! anyone of IV, $ anyone of LM, % anyone of FY, # anyone of NDQEBZ).

Figure 6.
Figure 6. Genomic organisation and transfection of muscle ponsin. (a) Schematic drawing of the organisation of the human ponsin gene. Each box represents an exon, alternatively spliced exons are highlighted by grey shading and numbers (A1). The second drawing illustrates which exons are represented in the splice variant of ponsin cloned from skeletal muscle cells (A2). The portions encoding sorbin homology regions (SoHo), the SH3 domains and a 278 aa long muscle-specific insertion in the C terminus (sinuous line) are indicated. The resulting full-length protein (Ps FL, A3) is shown subsequently. In addition, schematic drawings of deletion constructs used for transient transfection experiments are given: an N-terminal construct containing the sorbin homology region (Ps N-Ex25, A4), a construct compromising the entire C terminus (Ps SH3.1-C, A5) and a construct that consists only of the three C-terminal SH3 domains, but lacks the insertion (Ps SH3.1-C ΔEx30,31, A6). (b) Transient transfection of ponsin constructs into neonatal rat cardiomyocytes. Cells were transfected using either the GFP-tagged full-length muscle ponsin isoform (Ps FL, a–d), the N-terminal construct (Ps N-Ex25, e–h), the C-terminal ponsin construct (Ps SH3.1-C, i–m), the C-terminal ponsin construct lacking the insertion (Ps SH3.1-C ΔEx30,31, n–q) or GFP alone (r–u), respectively. At 48 h post transfection cells were triple labeled for paxillin (b, f, k, o, s) and a marker for intercalated disc structures (β-catenin; c, g, l, p, t). The C-terminal constructs that contained the three SH3 domains (i and n), co-localised with endogenous paxillin at cell–matrix contacts. In contrast, the N-terminal ponsin construct (e) was targeted predominantly to the nucleus. Note that paxillin was not observed in intercalated disc structures as delineated by β-catenin. Scale bar represents 10 μm.

The above figures are reprinted by permission from Elsevier: J Mol Biol (2007, 369, 665-682) copyright 2007.

Figures were selected by the author.