KBTBD13 is an actin-binding protein that modulates muscle kinetics
Josine M. de Winter, … , Nicol C. Voermans, Coen A.C. Ottenheijm
Josine M. de Winter, … , Nicol C. Voermans, Coen A.C. Ottenheijm
Published February 18, 2020; First published October 31, 2019
Citation Information: J Clin Invest. 2020;130(2):754-767. https://doi.org/10.1172/JCI124000.
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Research Article Muscle biology

KBTBD13 is an actin-binding protein that modulates muscle kinetics

Abstract

The mechanisms that modulate the kinetics of muscle relaxation are critically important for muscle function. A prime example of the impact of impaired relaxation kinetics is nemaline myopathy caused by mutations in KBTBD13 (NEM6). In addition to weakness, NEM6 patients have slow muscle relaxation, compromising contractility and daily life activities. The role of KBTBD13 in muscle is unknown, and the pathomechanism underlying NEM6 is undetermined. A combination of transcranial magnetic stimulation–induced muscle relaxation, muscle fiber– and sarcomere-contractility assays, low-angle x-ray diffraction, and superresolution microscopy revealed that the impaired muscle-relaxation kinetics in NEM6 patients are caused by structural changes in the thin filament, a sarcomeric microstructure. Using homology modeling and binding and contractility assays with recombinant KBTBD13, Kbtbd13-knockout and Kbtbd13R408C-knockin mouse models, and a GFP-labeled Kbtbd13-transgenic zebrafish model, we discovered that KBTBD13 binds to actin — a major constituent of the thin filament — and that mutations in KBTBD13 cause structural changes impairing muscle-relaxation kinetics. We propose that this actin-based impaired relaxation is central to NEM6 pathology.

Authors

Josine M. de Winter, Joery P. Molenaar, Michaela Yuen, Robbert van der Pijl, Shengyi Shen, Stefan Conijn, Martijn van de Locht, Menne Willigenburg, Sylvia J.P. Bogaards, Esmee S.B. van Kleef, Saskia Lassche, Malin Persson, Dilson E. Rassier, Tamar E. Sztal, Avnika A. Ruparelia, Viola Oorschot, Georg Ramm, Thomas E. Hall, Zherui Xiong, Christopher N. Johnson, Frank Li, Balazs Kiss, Noelia Lozano-Vidal, Reinier A. Boon, Manuela Marabita, Leonardo Nogara, Bert Blaauw, Richard J. Rodenburg, Benno Küsters, Jonne Doorduin, Alan H. Beggs, Henk Granzier, Ken Campbell, Weikang Ma, Thomas Irving, Edoardo Malfatti, Norma B. Romero, Robert J. Bryson-Richardson, Baziel G.M. van Engelen, Nicol C. Voermans, Coen A.C. Ottenheijm

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Figure 4

Determination of the nanostructure of muscle fibers.

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Determination of the nanostructure of muscle fibers. (A, top) Image of 2...
(A, top) Image of 28 NEM6 muscle fibers mounted and aligned in 1 plane between 2 halves of an EM grid (bottom); typical example of the resulting low-angle x-ray diffraction pattern. Note the well-resolved equatorial and meridional reflections. (B, left) Schematic of a sarcomere and the thin and thick filament, highlighting the structures that underlie the ALL6 reflection and the myosin (M6) reflection; (right) schematic representation of a cross section of muscle (thin filament in yellow, thick filament in pink), indicating the 1,0 and the 1,1 reflections. (C) No change in M6 reflection (thick-filament backbone periodicity) is observed in fibers of NEM6 patients compared with those of controls. (D) The ALL6 reflection is reduced in NEM6 fibers compared with control fibers. The green circles and white circles correspond to NEM6 patients harboring the KBTBD13E83Q mutation and the KBTBD13R408C mutation, respectively. Student’s t tests or Mann-Whitney U tests were performed between NEM6 and controls. *P < 0.05. For detailed information on the number of samples and statistical tests and outcomes, please see Supplemental Table 1.