Mechanics of Z-disc Proteins
Final Report Abstract
In this project, we used single molecule measurements by optical tweezers to study the binding mechanics of important constituents oft he muscle Z-disc. One part of the project was concerned with the binding mechanics of the actin binding domains of α-actinin and filamin to actin, while in the other sub-project, we investigated the binding oft he camodulin-like domain of α-actinin to the Z- repeats of titin. In the first subproject, we investigated the origin of the catch-bond mechanism of filamin A in contrast to the slip bond that α-actinin forms with actin. These differences are surprising because of the high homology of their actin binding domains. Using a mini filamin with only two rod domains we could rule out the contribution of other domains apart from the ABD to the catch-bond mechanism. A chimera mutant where we grafted the linker between the two CH domains from filamin into αactinin was sufficient to convert the actin binding characteristics from slip bond to catch bond. Using point mutations we could show that it is the flexibility of the linker together with interactions between the CH domains that are crucial for catch-bond vs slip-bond behavior. Stable anchoring of titin within the muscle Z-disc is essential for preserving muscle integrity during passive stretching. One of the main candidates for anchoring titin in the Z-disc is the actin crosslinker α-actinin. The calmodulin-like domain of α-actinin binds to the Z-repeats of titin. However, the mechanical and kinetic properties of this important interaction are still unknown. In the second part oft he project, we use a dual-beam optical tweezers assay to study the mechanics of this interaction at the single-molecule level. A single interaction of α-actinin and titin turns out to be surprisingly weak if force is applied. Depending on the direction of force application, the unbinding forces can more than triple. Our results suggest a model where multiple α-actinin/Z-repeat interactions cooperate to ensure long-term stable titin anchoring while allowing the individual components to exchange dynamically.
Publications
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Fast-folding alphahelices as reversible strain absorbers in the muscle protein myomesin. Proc Natl Acad Sci USA 2011; 108: 14139-14144
Berkemeier F, Bertz M, Xiao S, Pinotsis N, Wilmanns M, Gräter F, Rief M
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Dynamic force sensing of filamin revealed in single-molecule experiments. Proc Natl Acad Sci USA 2012; 109: 19679-19684
Rognoni L, Stigler J, Pelz B, Ylänne J, Rief M
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Superhelical architecture of the Myosin filament-linking protein myomesin with unusual elastic properties. PLoS Biol 2012; 10: e1001261
Pinotsis N, Chatziefthimiou SD, Berkemeier F, Beuron F, Mavridis IM, Konarev PV, Svergun DI, Morris E, Rief M, Wilmanns M
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Force-dependent isomerization kinetics of a highly conserved proline switch modulates the mechanosensing region of filamin. Proc Natl Acad Sci USA 2014; 111: 5568-5573
Rognoni L, Most T, Zoldak G, Rief M
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alpha-Actinin/titin interaction: A dynamic and mechanically stable cluster of bonds in the muscle Z-disk. Proc Natl Acad Sci USA 2017; 114: 1015-1020
Grison M, Merkel U, Kostan J, Djinovic-Carugo K, Rief M
