Multiple Sequence Variants in STAC3 Affect Interactions with Ca_V1.1 and Excitation-Contraction Coupling

Area of Science:

• Biochemistry
• Molecular Biology
• Genetics

Background:

• STAC3 protein is crucial for skeletal muscle excitation-contraction (EC) coupling.
• It interacts with the Ca_V1.1 channel via its tandem SH3 domains.
• A specific mutation (W284S) in STAC3 causes Native American myopathy.

Purpose of the Study:

• To determine the structural basis of STAC3 function.
• To investigate the impact of disease-associated STAC3 variants on protein function and muscle physiology.
• To understand the role of STAC3 in skeletal muscle EC coupling.

Main Methods:

• X-ray crystallography was used to determine the structure of human STAC3 tandem SH3 domains.
• The binding affinity of STAC3 variants to the Ca_V1.1 II-III loop was analyzed.
• The effect of variants on muscle EC coupling was assessed.

Main Results:

• The crystal structure of human STAC3 tandem SH3 domains was elucidated.
• Five disease-associated STAC3 variants were analyzed for their effects on binding and EC coupling.
• Variants W284S, F295L, and K329N were found to impair both STAC3 binding to Ca_V1.1 and muscle EC coupling.
• The K329N variant's impact highlights the functional importance of the second SH3 domain in STAC3-Ca_V1.1 interaction.

Conclusions:

• Multiple STAC3 variants, beyond W284S, can cause myopathy by disrupting skeletal muscle EC coupling.
• Both SH3 domains of STAC3 are important for its interaction with Ca_V1.1.
• Understanding STAC3 structure-function relationships is key to diagnosing and potentially treating myopathies.