KBTBD13 is an actin-binding protein that modulates muscle kinetics

Area of Science:

• Muscle physiology
• Molecular biology
• Genetics

Background:

• Muscle relaxation kinetics are crucial for muscle function.
• Nemaline myopathy (NEM6), caused by KBTBD13 mutations, presents with muscle weakness and slow relaxation.
• The precise role of KBTBD13 and the mechanism of NEM6 remain unclear.

Purpose of the Study:

• To elucidate the function of KBTBD13 in muscle.
• To determine the pathomechanism underlying nemaline myopathy type 6 (NEM6).
• To investigate the structural basis of impaired muscle relaxation in NEM6.

Main Methods:

• Utilized transcranial magnetic stimulation, muscle fiber and sarcomere contractility assays, low-angle X-ray diffraction, and superresolution microscopy.
• Employed homology modeling, binding and contractility assays with recombinant KBTBD13.
• Generated and analyzed Kbtbd13-knockout and Kbtbd13R408C-knockin mouse models, and a GFP-labeled Kbtbd13-transgenic zebrafish model.

Main Results:

• Demonstrated that KBTBD13 directly binds to actin, a key component of the muscle thin filament.
• Identified structural alterations in the thin filament caused by KBTBD13 mutations.
• Confirmed that these structural changes are responsible for the impaired muscle-relaxation kinetics observed in NEM6.

Conclusions:

• KBTBD13 plays a critical role in regulating muscle relaxation kinetics.
• Mutations in KBTBD13 lead to structural defects in the actin-based thin filament.
• Actin-based impaired relaxation is proposed as the central mechanism in NEM6 pathology.