PDBsum entry 2wa7

Structural protein

PDB id: 2wa7

Contents

Protein chain

225 a.a.

Ligands

CAC

CO3 ×3

Waters ×204

References listed in PDB file

Key reference

Title

Disease-Associated substitutions in the filamin b actin binding domain confer enhanced actin binding affinity in the absence of major structural disturbance: insights from the crystal structures of filamin b actin binding domains.

Authors

G.M.Sawyer, A.R.Clark, S.P.Robertson, A.J.Sutherland-Smith.

Ref.

J Mol Biol, 2009, 390, 1030-1047. [DOI no: 10.1016/j.jmb.2009.06.009]

PubMed id

19505475

Abstract

Missense mutations in filamin B (FLNB) are associated with the autosomal dominant atelosteogenesis (AO) and the Larsen group of skeletal malformation disorders. These mutations cluster in particular FLNB protein domains and act in a presumptive gain-of-function mechanism. In contrast the loss-of-function disorder, spondylocarpotarsal synostosis syndrome, is characterised by the complete absence of FLNB. One cluster of AO missense mutations is found within the second of two calponin homology (CH) domains that create a functional actin-binding domain (ABD). This N-terminal ABD is required for filamin F-actin crosslinking activity, a crucial aspect of filamin's role of integrating cell-signalling events with cellular scaffolding and mechanoprotection. This study characterises the wild type FLNB ABD and investigates the effects of two disease-associated mutations on the structure and function of the FLNB ABD that could explain a gain-of-function mechanism for the AO diseases. We have determined high-resolution X-ray crystal structures of the human filamin B wild type ABD, plus W148R and M202V mutants. All three structures display the classic compact monomeric conformation for the ABD with the CH1 and CH2 domains in close contact. The conservation of tertiary structure in the presence of these mutations shows that the compact ABD conformation is stable to the sequence substitutions. In solution the mutant ABDs display reduced melting temperatures (by 6-7 degrees C) as determined by differential scanning fluorimetry. Characterisation of the wild type and mutant ABD F-actin binding activities via co-sedimentation assays shows that the mutant FLNB ABDs have increased F-actin binding affinities, with dissociation constants of 2.0 microM (W148R) and 0.56 microM (M202V), compared to the wild type ABD K(d) of 7.0 microM. The increased F-actin binding affinity of the mutants presents a biochemical mechanism that differentiates the autosomal dominant gain-of-function FLNB disorders from those that arise through the complete loss of FLNB protein.

Figure 2.
Fig. 2. Cartoon representation of the wild type filamin B actin-binding domain. The structure is colour-coded with the N-terminal CH1 domain blue and the C-terminal CH2 domain red. The actin-binding sites (ABS1, ABS2, and ABS3) are coloured yellow. The major helices and the N and C termini are labelled in addition to the ends of the linker region (orange) between CH1 and CH2, which is not observed in the crystal structure (Glu131–Lys138).

Figure 8.
Fig. 8. Superposition of the filamin B wild type and α-actinin-4 (K255E) structures. Superposition of the wild type FLNB (blue) and α-actinin-4 K255E (red) ABD structures shown in Cα trace representation. The sidechains of FLNB W148 (orange) and M202 (green), and those of α-actinin-4 E255, T259 and S262 (all cyan) are shown in stick representation.

The above figures are reprinted by permission from Elsevier: J Mol Biol (2009, 390, 1030-1047) copyright 2009.