Actin - general

Author: Nat Pernick, M.D. (see Authors page)

Revised: 3 November 2015, last major update September 2013

Copyright: (c) 2003-2015,, Inc.

PubMed Search: actin[title]
  • Globular protein that forms microfilaments; found in all eukaryotic cells except nematode sperm (Wikipedia)
  • Highly conserved, differs by at most 20% between algae and humans
  • Participates in more protein-protein interactions than any known protein
  • The monomeric subunit of microfilaments, one of 3 major components of cytoskeleton (also microtubules and intermediate filaments); also a component of thin filaments (part of contractile apparatus of muscle cells)
  • Can transition between monomeric (G-actin) and filamentous (F-actin) states under control of nucleotide hydrolysis, ions, and actin-binding proteins (Annu Rev Biophys 2011;40:169)
  • Mammalian muscle cells contain alpha and gamma smooth muscle actin, alpha cardiac actin and alpha skeletal actin
  • Mammalian nonmuscle cells contain beta cytoplasmic actin and gamma cytoplasmic actin
  • Functions in all cells:
    • Forms part of cytoskeleton, which gives mechanical support to cell and is part of signal transduction
    • Assists with motility and phagocytosis
    • Helps myosins transport organelles and other substances through cell
    • Actin cytoskeleton may act as sensor and mediator of apoptosis (Bioarchitecture 2012;2:75)
  • Function in muscle cells: contraction
  • Actin cap: recently characterized cytoskeletal organelle composed of thick and highly contractile acto-myosin filaments anchored to apical surface of interphase nucleus (Soft Matter 2013;9:5516)
Clinical Features
  • Persistence of high titers of anti-actin serum antibodies is associated with disease activity in autoimmune hepatitis (Hepatology 2013;59:592)

Images hosted on other servers:

Actin and myosin in muscle

Helical structure of F-actin

G-actin to F-actin transition

Animation of muscle contraction

Micro Images

Various images