Question

Actin is one of the most evolutionarily conserved proteins. What does this tell you about the structure and function of this protein in eukaryotic cells?

Answer 1

Ans- Actin protein function in eukaryotic cell. Actin is one of the most abundant and highly conserved proteins found in all eukaryotic cells. The 43-kDa monomer of conventional actin (globular actin, or G-actin) spontaneously assembles in vitro to form long linear or branched structures (filamentous actin, or F-actin) upon the addition of salt, provided that ATP is present . The filaments polymerize noncovalently from both ends, with different affinities for the addition of monomers at each end. This results in an intrinsic polarity in the filament, in the form of a slow-growing end (minus end) and a fast-growing end (plus end). At steady state, the loss of subunits at the minus end and the equivalent gain at the plus end give rise to an effect known as treadmilling . Actin microfilaments are thin and flexible, and they rarely occur in isolation within the cell but, rather, in cross-linked aggregates and bundles. In vivo, they can form either stable or labile structures. Actin polymerization is a highly regulated process controlled both by nucleotide binding and hydrolysis and by the action of a number of actin-binding proteins that can cross-link, nucleate, cleave, bundle, stabilize, or destabilize the filaments.  

# Structure of this protein is- Each actin (thin) filament is made of two 'F' (filamentous) actins helically wound to each other . Each 'F' actin is a polymer of monomeric 'G' (globular) actins. Two filaments of another protein . A complex protein Troponin is distributed at regular intervals on the tropomyosin .

Troponin Tropomyosin F actin