RGD Reference Report - Structural requirements of tropomodulin for tropomyosin binding and actin filament capping. - Rat Genome Database

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Structural requirements of tropomodulin for tropomyosin binding and actin filament capping.

Authors: Kostyukova, AS  Rapp, BA  Choy, A  Greenfield, NJ  Hitchcock-DeGregori, SE 
Citation: Kostyukova AS, etal., Biochemistry. 2005 Mar 29;44(12):4905-10.
RGD ID: 1600523
Pubmed: (View Article at PubMed) PMID:15779917
DOI: Full-text: DOI:10.1021/bi047468p

Regulation of actin filament dynamics underlies many cellular functions. Tropomodulin together with tropomyosin can cap the pointed, slowly polymerizing, filament end, inhibiting addition or loss of actin monomers. Tropomodulin has an unstructured N-terminal region that binds tropomyosin and a folded C-terminal domain with six leucine-rich repeats. Of tropomodulin 1's 359 amino acids, an N-terminal fragment (Tmod1(1)(-)(92)) suffices for in vitro function, even though the C-terminal domain can weakly cap filaments independent of tropomyosin. Except for one short alpha-helix with coiled coil propensity (residues 24-35), the Tmod1(1)(-)(92) solution structure shows that the fragment is disordered and highly flexible. On the basis of the solution structure and predicted secondary structure, we have introduced a series of mutations to determine the structural requirements for tropomyosin binding (using native gels and CD) and filament capping (by measuring actin polymerization using pyrene fluorescence). Tmod1(1)(-)(92) fragments with mutations of an interface hydrophobic residue, L27G and L27E, designed to destroy the alpha-helix or coiled coil propensity, lost binding ability to tropomyosin but retained partial capping function in the presence of tropomyosin. Replacement of a flexible region with alpha-helical residues (residues 59-61 mutated to Ala) had no effect on tropomyosin binding but inhibited the capping function. A mutation in a region predicted to be an amphipathic helix (residues 65-75), L71D, destroyed the capping function. The results suggest that molecular flexibility and binding to actin via an amphipathic helix are both required for tropomyosin-dependent capping of the pointed end of the actin filament.

Gene Ontology Annotations    

Biological Process

Molecular Function

Objects Annotated

Genes (Rattus norvegicus)
Tpm1  (tropomyosin 1)
Tpm1_v7  (tropomyosin 1, variant 7)

Objects referenced in this article
Gene Tpm1_v1 tropomyosin 1, variant 1 Rattus norvegicus
Gene Tpm1_v2 tropomyosin 1, variant 2 Rattus norvegicus
Gene Tpm1_v3 tropomyosin 1, variant 3 Rattus norvegicus
Gene Tpm1_v4 tropomyosin 1, variant 4 Rattus norvegicus
Gene Tpm1_v5 tropomyosin 1, variant 5 Rattus norvegicus
Gene Tpm1_v6 tropomyosin 1, variant 6 Rattus norvegicus
Gene Tpm1_v8 tropomyosin 1, variant 8 Rattus norvegicus
Gene Tpm1_v9 tropomyosin 1, variant 9 Rattus norvegicus

Additional Information