Let's study ID: more irreducible complexity (Introduction)

by David Turell @, Tuesday, December 21, 2021, 15:41 (30 days ago) @ David Turell

Transporting heme is such an example:

https://phys.org/news/2021-12-pathway-emerges-biologists-function-heme.html

"Heme is an essential part of the protein hemoglobin, which colors human blood red. Heme also is crucial for cytochrome proteins, which power the cell. Humans, animals, plants and bacteria all use heme. (my bold)

"Hemoglobin shuttles oxygen to tissues where it is needed, while cytochromes carry electrons for energy conversion in the cell. But understanding how heme moves across membranes—like it needs to, in order to insert into hemoglobin and cytochromes—has been challenging. Heme transport is transient, which means heme moves through membranes quickly and leaves behind no traces. And heme-binding membrane proteins are difficult to purify in large quantities.

"In research published Dec. 20 in Nature Chemical Biology, scientists at Washington University in St. Louis described for the first time the structure of a bifunctional protein, called CcsBA, that transports heme and attaches it to cytochromes. The study led by Robert Kranz, professor of biology in Arts & Sciences, captured two conformational states of CcsBA, a bacterial and chloroplast protein, allowing scientists to characterize the enzyme mechanism.

""This new paper addresses the structural basis for how the CcsBA machine functions, revealing major dynamic switches that occur during the cycle of heme transport," Kranz said.

***

"The cyro-EM data identified two states in which either one or two heme molecules were bound.

"'The structural models we were able to construct illustrate that CcsBA is trapped with heme in two different conformations, which we term the closed and open states," Kranz said. "This new body of work addresses the structural basis by which the CcsBA machine functions, revealing a major dynamic switch that occurs during the transport cycle. (my bold)

"'One of the coolest findings is that a large chamber opens upon heme transport," he said. The chamber is for cytochrome c synthesis."

Comment: Note my bolds. Heme must be present to make the proteins that power cells. This is irreducible complexity. Only in the whole form does it work. It cannot be built in consecutive stages of evolution. Cells need it intact tov function. Only a designed process developed in one step can create this. Not by chance.


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