Question

Understand the structure and role of:

o Actin filaments: aka microfilaments, helical polymer, found near the plasma membrane, microvilli, and striated muscle, role of fimbrin vs. alpha-actinin vs. filamin, diseases that may come from mutations in actin filament proteins

Answer 1

Actin filaments are polar structures composed of globular molecules of actin arranged as a helix. They work in networks and bundles, often found just beneath the plasma membrane, where they crosslink to form the cell cortex. Actin filaments can be arranged in bundles or networks using various kinds of crosslink proteins. The bundles and networks are important for muscle contraction, cell shape, and cell adhesion.owing to the close proximity of its tandem actin-binding domains, fimbrin directs the formation of tightly bundled actin filaments that participate in dynamic processes, including cytokinesis in yeast and host cell invasion by enteropathic bacteria.Filamin binds all actin isoforms (e.g. F-actin, G-actin) and its structural organization allows it to form a flexible bridge between two actin filaments at various angles, thereby imparting the actin network with loose or gel-like qualities.Actin-accumulation myopathy is caused by a mutation in the ACTA1 gene. This gene provides instructions for making a protein called skeletal alpha (α)-actin, which is a member of the actin protein family found in skeletal muscles.Point mutations in vascular smooth muscle α-actin are the most prevalent cause of familial thoracic aortic aneurysms leading to acute dissections.