Cell complexity: DNA supply control enzyme complexity (Introduction)

by David Turell , Wednesday, February 21, 2018, 01:48 (2469 days ago) @ David Turell

The structure of an enzyme that controls the supply of DNA parts for cell use has been outlined:

https://phys.org/news/2018-02-scientists-high-resolution-glimpse-enzyme.html

"Using a state-of-the-art type of electron microscopy, an MIT-led team has discovered the structure of an enzyme that is crucial for maintaining an adequate supply of DNA building blocks in human cells.

"Their new structure also reveals the likely mechanism for how cells regulate the enzyme, known as ribonucleotide reductase (RNR). Significantly, the mechanism appears to differ from that of the bacterial version of the enzyme,

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"The RNR enzyme, which is found in all living cells, converts ribonucleotides (the building blocks of RNA) to deoxyribonucleotides (the building blocks of DNA). Cells must keep a sufficient stockpile of these building blocks, but when they accumulate too many, RNR is shut off by a deoxynucleotide molecule known as dATP. When more deoxynucleotides are needed, a related molecule called ATP binds to RNR and turns it back on.

"An unusual feature of RNR is that it can catalyze the production of four different products: the nucleotide bases often abbreviated as A, G, C, and T. In 2016, Drennan discovered that the enzyme achieves this by changing its shape in response to regulatory molecules.

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"Using cryo-EM, the MIT team found that the human version of the enzyme forms a ring made from six of the alpha subunits. When ATP, which activates RNR, is bound to the enzyme, the ring is unstable and can be easily opened up, allowing the beta subunit to make its way into the ring. This joining of alpha and beta allows the enzyme's active site, located in the beta subunit, to perform the chemical reactions necessary to produce deoxynucleotides.

"However, when the inhibitor dATP is present, the ring becomes much more rigid and does not allow the beta subunit to enter. This prevents the enzyme from catalyzing the production of deoxynucleotides."

To see these complex structures look at the illustrations in this article:

https://elifesciences.org/articles/31502

Comment: The complexity of the structure and of the functions of this giant enzyme demands that a designer of life be strongly considered. Only a planning mind can create such structures with such precise mechanisms of function.