Genome complexity: chaperones for histones (Introduction)

by David Turell , Tuesday, January 07, 2020, 19:28 (1570 days ago) @ David Turell

Coiling DNA around histone spools requires chaperone molecules, one of which uses ATP for energy:

https://www.sciencedaily.com/releases/2020/01/200107104936.htm

"The genetic material of our cells -- DNA -- exists in a high-order structure called "chromatin." Chromatin consists of DNA wrapped around histone proteins and efficiently packs DNA into a small volume. Moreover, using a spool and thread analogy, chromatin allows DNA to be locally wound or unwound, thus enabling genes to be enclosed or exposed.

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'"In order to carefully control the assembly and disassembly of chromatin units, histone chaperones act as molecular escorts that prevent histone aggregation and undesired interactions,"

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"Song and his team looked to Abo1, the only known histone chaperone that utilizes cellular energy (ATP). While Abo1 is found in yeast, it has an analogous partner in other organisms, including humans, called ATAD2. Both use ATP, which is produced through a cellular process where enzymes break down a molecule's phosphate bond. ATP energy is typically used to power other cellular processes, but it is a rare partner for histone chaperones.

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"The researchers found through real-time observation that Abo1 is ring-shaped and changes its structure to accommodate a specific histone and deposit it on DNA. Moreover, they found that the accommodating structural changes are powered by ADP.

"'We discovered a mechanism by which Abo1 accommodates histone substrates, ultimately allowing it to function as a unique energy-dependent histone chaperone," Song said. "We also found that despite looking like a protein disassembly machine, Abo1 actually loads histone substrates onto DNA to facilitate chromatin assembly.'"

Comment: Once again we see a very complex control mechanism using very specific proteins which have a very specific function ability. It cannot be assembled stepwise but all at once, since it is irreducibly complex, and all parts have to be designed and put together at the same time.