# Oligomer-dependent and oligomer-independent pathogenesis of muscular dystrophy-associated mutations within the penta-EF-hand domain of calpain-3[image]

## TL;DR

This study explores how mutations in the PEF domain of calpain-3 cause muscular dystrophy through two distinct mechanisms.

## Contribution

The study identifies both oligomer-dependent and oligomer-independent pathways in LGMDR1 pathogenesis.

## Key findings

- Oligomer formation of CAPN3 through the PEF domain is crucial for efficient autolytic processing.
- LGMDR1 mutants fail to localize at sarcomeric M-bands due to reduced titin binding, independent of oligomerization.
- Mutations in the PEF domain disrupt CAPN3's physiological function via two distinct mechanisms.

## Abstract

Limb-girdle muscular dystrophy R1 (LGMDR1) is an autosomal recessive disorder caused by dysfunction of calpain-3 (CAPN3; also known as p94), a muscle-specific, Ca2+-dependent cysteine protease. LGMDR1 mutations are distributed throughout the Capn3 gene. Nevertheless, our knowledge of the biochemical and biological properties of individual LGMDR1 mutants is limited, hindering a full understanding of LGMDR1 pathogenesis. Here, we comprehensively examined the functional properties of LGMDR1 mutants within the penta-EF-hand (PEF) domain at the COOH terminus of CAPN3, focusing on their autolytic processing, oligomerization, titin binding, and subcellular localization within sarcomeres of mouse skeletal muscle. We found that oligomer formation of CAPN3 through the PEF domain contributes to efficient NH2-terminal and IS1-region processing, which were impaired by specific LGMDR1 mutations within the PEF domain. Furthermore, while WT CAPN3 predominantly localized at the sarcomeric M-bands of tibialis anterior muscles in vivo, several LGMDR1 mutants were absent from the M-bands due to decreased binding to titin, a giant cytoskeletal protein, irrespective of their oligomerization status. These findings indicate that LGMDR1 mutations within the PEF domain disrupt the physiological function of CAPN3 through both oligomer-dependent and oligomer-independent mechanisms, highlighting two distinct pathways contributing to LGMDR1 pathogenesis.