Nanosurgical Manipulation of Titin and Its M-Complex

Abstract

Titin is a multifunctional filamentous protein anchored in the M-band, a hexagonally organized supramolecular lattice in the middle of the muscle sarcomere. Functionally, the M-band is a framework that cross-links myosin thick filaments, organizes associated proteins, and maintains sarcomeric symmetry via its structural and putative mechanical properties. Part of the M-band appears at the C-terminal end of isolated titin molecules in the form of a globular head, named here the “M-complex”, which also serves as the point of head-to-head attachment of titin. We used high-resolution atomic force microscopy and nanosurgical manipulation to investigate the topographical and internal structure and local mechanical properties of the M-complex and its associated titin molecules. We find that the M-complex is a stable structure that corresponds to the transverse unit of the M-band organized around the myosin thick filament. M-complexes may be interlinked into an M-complex array that reflects the local structural and mechanical status of the transversal M-band lattice. Local segments of titin and the M-complex could be nanosurgically manipulated to achieve extension and domain unfolding. Long threads could be pulled out of the M-complex, suggesting that it is a compact supramolecular reservoir of extensible filaments. Nanosurgery evoked an unexpected volume increment in the M-complex, which may be related to its function as a mechanical spacer. The M-complex thus displays both elastic and plastic properties which support the idea that the M-band may be involved in mechanical functions within the muscle sarcomere.

Structural hierarchy of mechanical extensibility in human von Willebrand factor multimers

“…Rather, the contracted protomer (PR1) was more frequently found at the ends of the multimer, while the highly extended protomers (PR6, PR7) were in the middle (Figures 6g–i , S3 ). The centrally located overstretch of an extended object, called necking, is characteristic of plastic behavior and has been found in biomolecular systems (Sziklai et al, 2022 ). Although necking arises in systems held firmly at both ends, we speculate that just prior to the departure of the receding meniscus from the surface of the stretched VWF multimer, such a mechanical geometry is present, albeit for a short period of time.…”

O-GlcNAcylation: The Underestimated Emerging Regulators of Skeletal Muscle Physiology

“…O -GlcNAcylation of α/β-crystallin at Thr 170 and Thr 162 regulates its localization and its interaction with desmin, respectively [ 255 , 256 ]. The multiple O -GlcNAcylation sites of mouse titin are located on the kelch-12 domain, and the absence of titin leads to the change of muscle structure and the decrease of muscle performance [ 249 , 257 ]. These O -GlcNAcylation sites are located in the key regions of sarcomere assembly and myosin polymerization and its interaction with MyBP-C and MHC [ 258 , 259 ].…”

Investigation of the motion of fullerene-wheeled nano-machines on thermally activated curved gold substrates

“…A great number of methods are present for manipulating one molecule or a cluster of atoms on a surface 5 . However, there are some drawbacks to these methods contrasting with the performance of natural nano-manipulators 6 , 7 . First and foremost, they are not capable of working on abundant particles simultaneously 8 , and also, they are several orders of magnitude greater than the manipulated payloads 9 .…”