Cryo-EM Structures of the Actin:Tropomyosin Filament Reveal the Mechanism for the Transition from C- to M-State

Sousa, Duncan; Stagg, Scott M.; Stroupe, M. Elizabeth

doi:10.1016/j.jmb.2013.08.020

Cited by 27 publications

(23 citation statements)

References 57 publications

(89 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1C, c-closed) yielded a perfect match with the proposed model of the apo state (15,18). We found that the azimuthal position of Tpm on F-actin in the apo state (15,18) was very similar to the azimuthal position of Tpm on F-actin in the closed structural state obtained by the negative staining protocol here (SI Appendix, Fig. S1C) and by others (3,5).…”

Section: +supporting

confidence: 80%

See 1 more Smart Citation

CA2+-Induced Movement of Tropomyosin on Native Cardiac Thin Filaments Revealed by Cryoelectron Microscopy

Risi

Belknap

Heeley

et al. 2018

Biophysical Journal

View full text Add to dashboard Cite

Muscle contraction relies on the interaction of myosin motors with F-actin, which is regulated through a translocation of tropomyosin by the troponin complex in response to Ca 2+ . The current model of muscle regulation holds that at relaxing (low-Ca 2+ ) conditions tropomyosin blocks myosin binding sites on F-actin, whereas at activating (high-Ca 2+ ) conditions tropomyosin translocation only partially exposes myosin binding sites on F-actin so that binding of rigor myosin is required to fully activate the thin filament (TF). Here we used a single-particle approach to helical reconstruction of frozen hydrated native cardiac TFs under relaxing and activating conditions to reveal the azimuthal movement of the tropomyosin on the surface of the native cardiac TF upon Ca 2+ activation. We demonstrate that at either relaxing or activating conditions tropomyosin is not constrained in one structural state, but rather is distributed between three structural positions on the surface of the TF. We show that two of these tropomyosin positions restrain actomyosin interactions, whereas in the third position, which is significantly enhanced at high Ca 2+ , tropomyosin does not block myosin binding sites on F-actin. Our data provide a structural framework for the enhanced activation of the cardiac TF over the skeletal TF by Ca 2+ and lead to a mechanistic model for the regulation of the cardiac TF.thin filament | cardiac muscle regulation | cryoelectron microscopy

show abstract

Section: +supporting

confidence: 80%

“…First, we traced the movement of the inner Tpm strand upon the c-blocked → c-open → myosin transition, which was found to be a rocking movement around the anchor point (Fig. 3H, red arrow; SI Appendix, Movie S1) originally predicted by Sousa et al (18). Next, we compared the successive movement of the outer Tpm ɑ-helical strand.…”

Section: +mentioning

confidence: 87%

CA2+-Induced Movement of Tropomyosin on Native Cardiac Thin Filaments Revealed by Cryoelectron Microscopy

Risi

Belknap

Heeley

et al. 2018

Biophysical Journal

View full text Add to dashboard Cite

show abstract

“…Each thin filament is essentially an actin polymer. Tropomyosin (TM) is a long dimeric coiled coil protein that polymerizes in a head-to-tail manner to span most of the thin filament except at the Z-disc 148 . A single tropomyosin dimer spans seven actin monomers.…”

Section: Hypotensionmentioning

confidence: 99%

“…The deeply buried cTnI Ile148 residue is shown in space-filling spheres. d | The ternary complex of cNTnC, cTnI [147][148][149][150][151][152][153][154][155][156][157][158][159][160][161][162][163] and bepridil (shown in grey), showing bepridil bound to a deep hydrophobic pocket and displacing cTnI Ile148 (REF. 94).…”

mentioning

confidence: 99%

Targeting the sarcomere to correct muscle function

Hwang

Sykes

2015

Nat Rev Drug Discov

109

116

View full text Add to dashboard Cite

“…This approach is particularly attractive because an extensive body of work has allowed establishment of the subunit-subunit interfaces in the actin filament [Lorenz et al, 1995;Bobkov et al, 2002;Bubb et al, 2002;Oda et al, 2009;Fujii et al, 2010]. Similar work has also defined binding sites on the actin surface for a number of regulatory proteins and myosin Rayment et al, 1993;Schroder et al, 1993;Milligan, 1996;Wong et al, 1999;Behrmann et al, 2012;Sousa et al, 2013]. Conservation of actin structure and these sites across most actins allows one to postulate a likely effect of a particular mutation and then experimentally test the hypothesis.…”

Section: Rubenstein and Wenmentioning

confidence: 99%

Insights into the effects of disease‐causing mutations in human actins

Rubenstein

Wen

2014

Cytoskeleton

View full text Add to dashboard Cite

Mutations in all six actins in humans have now been shown to cause diseases. However, a number of factors have made it difficult to gain insight into how the changes in actin functions brought about by these pathogenic mutations result in the disease phenotype. These include the presence of multiple actins in the same cell, limited accessibility to pure mutant material, and complexities associated with the structures and their component cells that manifest the diseases. To try to circumvent these difficulties, investigators have turned to the use of model systems. This review describes these various approaches, the initial results obtained using them, and the insight they have provided into allosteric mechanisms that govern actin function. Although results so far have not explained a particular disease phenotype at the molecular level, they have provided valuable insight into actin function at the mechanistic level which can be utilized in the future to delineate the molecular bases of these different actinopathies. Key Words: actin; allostery; disease; mutation; isoforms Introduction A ctin mutations can cause human disease. However, little is known concerning the mechanisms by which these mutations lead to the disease phenotypes they produce. The goal of this review is to describe the general properties of actin, the diseases associated with mutations in actin, methodologies that might be employed to achieve a mechanistic understanding of actin based disease and efforts that have been made toward this goal. Properties of G-and F-ActinA discussion of the effects of pathogenic mutations on actin function requires a basic understanding of actin structure and its solution properties. Actin is an abundant 42 kD monomeric protein, found in virtually all eukaryotic cells, that can cycle between either a monomeric (G-actin) or polymeric (F-actin) state. It plays both contractile and structural roles in the cytoplasm, and recent studies have documented that actin in the nucleus acts as a promoter of transcription or as a member of a number of chromatin remodeling complexes Philimonenko et al., 2004;Miyamoto and Gurdon, 2011; Miyamoto et al., 2011a,b;Weston et al., 2012].G-actin is a clam-shaped protein with two domains, the inner and outer domains ( Fig. 1), connected by a hinge region, and separated by a deep cleft. Outer (subdomains 1 and 2) and inner (subdomains 3 and 4) refer to their position in the actin filament. The N and C-termini reside on opposite faces of the protein in subdomain 1. An adenine nucleotide binds deep within the inter-domain cleft, held in place by a divalent cation, and imparts stability to the protein and the filament. This latter role depends on its ability to cycle between the ATP and ADP state by virtue of a polymerization-dependent ATPase activity [Carlier et al., 1987;Korn et al., 1987]. F-actin is a polar structure with pointed (2) and barbed (1) ends referring to the arrowhead pattern formed when myosin S1 binds to F-actin in the absence of ATP [Craig et al., 1985]. The polarity of th...

show abstract

Cryo-EM Structures of the Actin:Tropomyosin Filament Reveal the Mechanism for the Transition from C- to M-State

Cited by 27 publications

References 57 publications

CA2+-Induced Movement of Tropomyosin on Native Cardiac Thin Filaments Revealed by Cryoelectron Microscopy

CA2+-Induced Movement of Tropomyosin on Native Cardiac Thin Filaments Revealed by Cryoelectron Microscopy

Targeting the sarcomere to correct muscle function

Insights into the effects of disease‐causing mutations in human actins

Contact Info

Product

Resources

About