Biophysical Society Thematic Meeting | Canterbury 2023

Towards a More Perfect Union: Multi-Scale Models of Muscle and Their Experimental Validation

Monday Speaker Abstracts

CUT AND PASTE OF MYOSIN BINDING PROTEIN-C IN SKELETAL MUSCLES Samantha P Harris 1 ; Nichlas M Engels 1 ; Rachel L Sadler 1 ; Michel Kuehn 2 ; Devin Nissen 3 ; Weikang Ma 3 ; Thomas Irving 3 ; Wolfgang A Linke 2 ; Anthony L Hessel 2 ; 1 University of Arizona, Physiology, Tucson, AZ, USA 2 University of Muenster, Institute of Physiology II, Muenster, Germany 3 Illinois Institute of Technology, BioCat, Department of Biology, Chicago, IL, USA The family of proteins known as myosin binding protein-C (MyBP-C) are regulatory proteins localized to muscle sarcomeres that are encoded by 3 separate genes (MYBPC1, MYBPC2, and MYBPC3). The 3 genes encode distinct MyBP-C protein paralogs expressed in fast skeletal, slow skeletal, and cardiac muscles, respectively. However, due to co-expression of the two skeletal paralogs (and their related multiple splice variants) it has been challenging to describe distinct functional roles for each MyBP-C because skeletal muscles typically express a mixture of fiber types. Here, we overcome this challenge by engineering two new mouse models that selectively target MYBPC1 and MYBPC2 to permit removal and replacement (cut and paste) of each protein paralog in permeabilized muscle fibers in situ. The objective of this study was to determine functional and structural effects of selective loss of fast skeletal and slow skeletal MyBP-C in predominantly slow twitch (soleus) and fast twitch (psoas), muscle respectively. Results of force measurements in soleus and psoas showed that tension-pCa relationships were right-shifted following treatment with TEVp, indicating reduced Ca 2+ sensitivity of tension following selective loss of either sMyBP-C or fMyBP-C. Notably, spontaneous contractile oscillations (SPOC) were also frequently observed following loss of MyBP-C. X-ray diffraction experiments in permeabilized psoas fibers showed significant changes in sarcomere structure including changes in lattice spacing, I 1,1 /I 1,0 ratios, and reflections attributable to both thick and thin filament structures (e.g., M3 and M6 spacing and A6 and A7 spacing, respectively). Conclusions: We interpret these data in terms of a model where the skeletal muscle paralogs of MyBP-C exert both structural and functional effects at rest and in contracting muscle, potentially by binding to both thick and thin filaments simultaneously.

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