F-actin cross-linking protein which is thought to anchor actin to a variety of intracellular structures. This is a bundling protein. Homodimer; antiparallel. Also forms heterodimers with ACTN2. Interacts with MYOZ1. Expressed only in a subset of type 2 skeletal muscle fibers. About 18% of the world population lack a functional ACTN3 due to a stop codon polymorphism at position 577. The absence of a functional ACTN3 expression is not correlated with a disease state [MIM:617749]. Belongs to the alpha-actinin family. According to the human genome assembly there is a stop codon in position 577 which is only found in 18% of the world population.