Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils. It is found in essentially all eukaryotic cells, where it may be present at a concentration of over 100 μM; its mass is roughly 42 kDa, with a diameter of 4 to 7 nm.
Fluorescence micrograph showing F-actin (in green) in rat fibroblasts
Structure of the C-terminal subdomain of villin, a protein capable of splitting microfilaments
Giant nemaline rods produced by the transfection of a DNA sequence of ACTA1, which is the carrier of a mutation responsible for nemaline myopathy
Position of seven mutations relevant to the various actinopathies related to ACTA1
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, providing structure to cells and organisms, and transporting molecules from one location to another. Proteins differ from one another primarily in their sequence of amino acids, which is dictated by the nucleotide sequence of their genes, and which usually results in protein folding into a specific 3D structure that determines its activity.
John Kendrew with model of myoglobin in progress
Proteins in different cellular compartments and structures tagged with green fluorescent protein (here, white)
Constituent amino-acids can be analyzed to predict secondary, tertiary and quaternary protein structure, in this case hemoglobin containing heme units
