Biological complexity: control of actin in cells (Introduction)

by David Turell , Thursday, April 09, 2020, 01:50 (1690 days ago) @ David Turell

One of the most prevalent of all molecules in cells. it forms the fibers that support the tra nsport of protein products i n cells:

https://phys.org/news/2020-04-advance-actin-cell-function.html

"The research shows how actin is modified, and should accelerate further research on how actin works and is regulated in cells. The researchers used X-ray crystallography and other advanced techniques to reveal the atomic-scale structure of actin as it is being modified by a partner enzyme during the attachment of a cluster of atoms, called an acetyl group, at the start of the chain of amino acids that forms the protein. The modification, called N-terminal acetylation, can occur on the vast majority of human proteins and is thought to have important biological functions. However, in the case of actin those functions have not been entirely clear.

***

"Actin's importance is underscored by the fact that in mammalian cells it is the most abundant protein in the cytoplasm, the space outside the nucleus. It is best known for forming cable-like structures called filaments, which make up much of the supportive "skeleton" of cells, and also play key roles in cell division and in cells' ability to move about in tissues.

"N-terminal acetylation can occur on actin, as it does on more than 80 percent of human proteins, and appears to help regulate actin's ability to form filaments. However, the precise functions of this modification have never been clear, and scientists—a team led by Dominguez and a team of collaborators at the University of Bergen in Norway led by Dr. Thomas Arnesen—discovered the enzyme that catalyzes actin N-terminal acetylation only in 2018.

***

"One of their key findings was that NAA80 does not recognize and acetylate actin when the protein is assembled into filaments. It does acetylate actin when it exists as a separate molecule, called a monomer. However, the most efficient N-terminal acetylation occurs when actin is bound to another protein called profilin—a known partner of actin, and one that is closely involved in actin's formation of filaments and like actin is also very abundant in the cell.

"'It was a surprise to us to find that this protein, NAA80, appears to have evolved to recognize not actin alone but the profilin-actin complex," Dominguez says. "It suggests that profilin has a role as a 'chaperone' that allows actin to be N-terminally acetylated prior to filament formation."

"One of their key findings was that NAA80 does not recognize and acetylate actin when the protein is assembled into filaments. It does acetylate actin when it exists as a separate molecule, called a monomer. However, the most efficient N-terminal acetylation occurs when actin is bound to another protein called profilin—a known partner of actin, and one that is closely involved in actin's formation of filaments and like actin is also very abundant in the cell.

"'It was a surprise to us to find that this protein, NAA80, appears to have evolved to recognize not actin alone but the profilin-actin complex," Dominguez says. "It suggests that profilin has a role as a 'chaperone' that allows actin to be N-terminally acetylated prior to filament formation.'"

Comment: Such a highly irreducibly complex system requiring specific enzymes must have been designed. It puts actin under precise formation control. There must be a designer