Actinin is a microfilament protein. α-Actinin is necessary for the attachment of actin filaments to the Z-lines in skeletal muscle cells, and to the dense bodies in smooth muscle cells. The functional protein is an anti-parallel dimer, which cross-links the thin filaments in adjacent sarcomeres, and therefore coordinated contractions between sarcomeres in the horizontal axis.
The non-sarcomeric α-actinins (ACTN1 and ACTN4) are widely expressed. Both ends of the rod-shaped α-actinin dimer contain actin-binding domains.
Mutations in ACTN4 can cause the kidney disease focal segmental glomerulosclerosis.
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