Dataset Information

The crystal structure of the C-terminal fragment of striated-muscle alpha-tropomyosin reveals a key troponin T recognition site.

ABSTRACT: Contraction in striated and cardiac muscles is regulated by the motions of a Ca(2+)-sensitive tropomyosin/troponin switch. In contrast, troponin is absent in other muscle types and in nonmuscle cells, and actomyosin regulation is myosin-linked. Here we report an unusual crystal structure at 2.7 A of the C-terminal 31 residues of rat striated-muscle alpha-tropomyosin (preceded by a fragment of the GCN4 leucine zipper). The C-terminal 22 residues (263-284) of the structure do not form a two-stranded alpha-helical coiled coil as does the rest of the molecule, but here the alpha-helices splay apart and are stabilized by the formation of a tail-to-tail dimer with a symmetry-related molecule. The site of splaying involves a small group of destabilizing core residues that is present only in striated muscle tropomyosin isoforms. These results reveal a specific recognition site for troponin T and clarify the physical basis for the unique regulatory mechanism of striated muscles.

SUBMITTER: Li Y

PROVIDER: S-EPMC124239 | biostudies-literature | 2002 May

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

The crystal structure of the C-terminal fragment of striated-muscle alpha-tropomyosin reveals a key troponin T recognition site.

Li Yu Y Mui Suet S Brown Jerry H JH Strand James J Reshetnikova Ludmilla L Tobacman Larry S LS Cohen Carolyn C

Proceedings of the National Academy of Sciences of the United States of America 20020501 11

Contraction in striated and cardiac muscles is regulated by the motions of a Ca(2+)-sensitive tropomyosin/troponin switch. In contrast, troponin is absent in other muscle types and in nonmuscle cells, and actomyosin regulation is myosin-linked. Here we report an unusual crystal structure at 2.7 A of the C-terminal 31 residues of rat striated-muscle alpha-tropomyosin (preceded by a fragment of the GCN4 leucine zipper). The C-terminal 22 residues (263-284) of the structure do not form a two-strand ...[more]

PMID: 12032291

Similar Datasets

Project description:Tropomyosin and troponin regulate muscle contraction by participating in a macromolecular scale steric-mechanism to control myosin-crossbridge - actin interactions and consequently contraction. At low-Ca2+, the C-terminal 30% of troponin subunit-I (TnI) is proposed to trap tropomyosin in a position on thin filaments that sterically interferes with myosin-binding, thus causing muscle relaxation. In contrast, at high-Ca2+, inhibition is released after the C-terminal domains dissociate from F-actin-tropomyosin as its component switch-peptide domain binds to the N-lobe of troponin-C (TnC). Recent, paradigm-shifting, cryo-EM reconstructions by the Namba group have revealed density attributed to TnI along cardiac muscle thin filaments at both low- and high-Ca2+ concentration. Modeling the reconstructions showed expected high-Ca2+ hydrophobic interactions of the TnI switch-peptide and TnC. However, under low-Ca2+ conditions, sparse interactions of TnI and tropomyosin, and in particular juxtaposition of non-polar switch-peptide residues and charged tropomyosin amino acids in the published model seem difficult to reconcile with an expected steric-blocking conformation. This anomaly is likely due to inaccurate fitting of tropomyosin into the cryo-EM volume. In the current study, the low-Ca2+ cryo-EM volume was fitted with a more accurate tropomyosin model and representation of cardiac TnI. Our results show that at low-Ca2+ a cluster of hydrophobic residues at the TnI switch-peptide and adjacent H4 helix (Ala149, Ala151, Met 154, Leu159, Gly160, Ala161, Ala163, Leu167, Leu169, Ala171, Leu173) draw-in tropomyosin surface residues (Ile143, Ile146, Ala151, Ile154), presumably attracting the entire tropomyosin cable to its myosin-blocking position on actin. The modeling confirms that neighboring TnI "inhibitory domain" residues (Arg145, Arg148) bind to thin filaments at actin residue Asp25, as previously suggested. ClusPro docking of TnI residues 137-184 to actin-tropomyosin, including the TnI inhibitory-domain, switch-peptide and Helix H4, verified the modeled configuration. Our residue-to-residue contact-mapping of the TnI-tropomyosin association lends itself to experimental validation and functional localization of disease-bearing mutations.

Dataset Information

The crystal structure of the C-terminal fragment of striated-muscle alpha-tropomyosin reveals a key troponin T recognition site.

Publications

The crystal structure of the C-terminal fragment of striated-muscle alpha-tropomyosin reveals a key troponin T recognition site.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets