Actin structure
•Folding of the actin
molecule is represented by ribbon tracing of
the a-carbon atoms. N and C correspond to the amino- and carboxyl-terminals, respectively. The letters
followed by numbers represent amino acids in the polypeptide chain. A hypothetical vertical line divides
the actin molecule into two domains
"large", left side, and "small",
right side. ATP and Ca2+ are located between the two domains.
These two domains can be subdivided further into two subdomains each, the small domain being
composed of subdomains 1 and 2, and the 2 has significantly
less mass than the other three subdomains and this is the reason of dividing actin into small and
large domains). The four subdomains are
held together and stabilized mainly by salt
bridges and hydrogen bonds to the phosphate
groups of the bound ATP and to its associated
Ca2+ localized in the center of the molecule.