title: Modeling the assembly of the multiple domains of α-actinin-4 and its role in actin cross-linking.
abstract: The assembly of proteins into multidomain complexes is critical for their function. In eukaryotic nonmuscle cells, regulation of the homodimeric actin cross-linking protein α-actinin-4 (ACTN4) during cell migration involves signaling receptors with intrinsic tyrosine kinase activity, yet the underlying molecular mechanisms are poorly understood. As a first step to address the latter, we validate here an atomic model for the ACTN4 end region, which corresponds to a ternary complex between the N-terminal actin-binding domain (ABD) and an adjacent helical neck region of one monomer, and the C-terminal calmodulin-like domain of the opposite antiparallel monomer. Mutagenesis experiments designed to disrupt this ternary complex confirm that its formation reduces binding to F-actin. Molecular dynamics simulations show that the phosphomimic mutation Y265E increases actin binding by breaking several interactions that tether the two calponin homology domains into a closed ABD conformation. Simulations also show a disorder-to-order transition in the double phosphomimic mutant Y4E/Y31E of the 45-residue ACTN4 N-terminal region, which can inhibit actin binding by latching both calponin homology domains more tightly. Collectively, these studies provide a starting point for understanding the role of external cues in regulating ACTN4, with different phenotypes resulting from changes in the multidomain assembly of the protein.
authors: Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors: Timothy
authors: T
authors: Travers
authors: Hanshuang
authors: H
authors: Shao
authors: Alan
authors: A
authors: Wells
authors: Carlos J
authors: CJ
authors: Camacho
mesh_terms: D000185:Actinin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001665:Binding Sites; D002135:Calcium-Binding Proteins / Q000378:metabolism; D006801:Humans; D008840:Microfilament Proteins / Q000378:metabolism; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D010641:Phenotype; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D000096985:Calponins
chemical_list: D000185:Actinin; D000199:Actins; D002135:Calcium-Binding Proteins; D008840:Microfilament Proteins; D000096985:Calponins; C111453:ACTN4 protein, human