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==Structure of upper Tn Ca2+ free (rotated) and lower Tn Ca2+ bound cardiac native thin filament at pCa=5.8==
<StructureSection load='7kon' size='340' side='right'caption='[[7kon]], [[Resolution|resolution]] 8.10&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[7kon]] is a 29 chain structure with sequence from [https://en.wikipedia.org/wiki/Sus_scrofa Sus scrofa]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=7KON OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=7KON FirstGlance]. <br>
</td></tr><tr id='method'><td class="sblockLbl"><b>[[Empirical_models|Method:]]</b></td><td class="sblockDat" id="methodDat">Electron Microscopy, [[Resolution|Resolution]] 8.1&#8491;</td></tr>
<tr id='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[https://proteopedia.org/fgij/fg.htm?mol=7kon FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=7kon OCA], [https://pdbe.org/7kon PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=7kon RCSB], [https://www.ebi.ac.uk/pdbsum/7kon PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=7kon ProSAT]</span></td></tr>
</table>
== Function ==
[https://www.uniprot.org/uniprot/TPM1_PIG TPM1_PIG] Binds to actin filaments in muscle and non-muscle cells. Plays a central role, in association with the troponin complex, in the calcium dependent regulation of vertebrate striated muscle contraction. Smooth muscle contraction is regulated by interaction with caldesmon. In non-muscle cells is implicated in stabilizing cytoskeleton actin filaments.
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== Publication Abstract from PubMed ==
Every heartbeat relies on cyclical interactions between myosin thick and actin thin filaments orchestrated by rising and falling Ca(2+) levels. Thin filaments are comprised of two actin strands, each harboring equally separated troponin complexes, which bind Ca(2+) to move tropomyosin cables away from the myosin binding sites and, thus, activate systolic contraction. Recently, structures of thin filaments obtained at low (pCa approximately 9) or high (pCa approximately 3) Ca(2+) levels revealed the transition between the Ca(2+)-free and Ca(2+)-bound states. However, in working cardiac muscle, Ca(2+) levels fluctuate at intermediate values between pCa approximately 6 and pCa approximately 7. The structure of the thin filament at physiological Ca(2+) levels is unknown. We used cryoelectron microscopy and statistical analysis to reveal the structure of the cardiac thin filament at systolic pCa = 5.8. We show that the two strands of the thin filament consist of a mixture of regulatory units, which are composed of Ca(2+)-free, Ca(2+)-bound, or mixed (e.g., Ca(2+) free on one side and Ca(2+) bound on the other side) troponin complexes. We traced troponin complex conformations along and across individual thin filaments to directly determine the structural composition of the cardiac native thin filament at systolic Ca(2+) levels. We demonstrate that the two thin filament strands are activated stochastically with short-range cooperativity evident only on one of the two strands. Our findings suggest a mechanism by which cardiac muscle is regulated by narrow range Ca(2+) fluctuations.

The structure of the native cardiac thin filament at systolic Ca(2+) levels.,Risi CM, Pepper I, Belknap B, Landim-Vieira M, White HD, Dryden K, Pinto JR, Chase PB, Galkin VE Proc Natl Acad Sci U S A. 2021 Mar 30;118(13):e2024288118. doi: , 10.1073/pnas.2024288118. PMID:33753506<ref>PMID:33753506</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
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<div class="pdbe-citations 7kon" style="background-color:#fffaf0;"></div>

==See Also==
*[[Actin 3D structures|Actin 3D structures]]
*[[Tropomyosin 3D structures|Tropomyosin 3D structures]]
*[[Troponin 3D structures|Troponin 3D structures]]
== References ==
<references/>
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</StructureSection>
[[Category: Large Structures]]
[[Category: Sus scrofa]]
[[Category: Galkin VE]]
[[Category: Risi CM]]