Bacterial motors carefully studied (Introduction)

by David Turell , Monday, July 05, 2021, 16:55 (1236 days ago) @ David Turell

The function of sensory cilia desscribed:

https://www.cell.com/current-biology/fulltext/S0960-9822(21)00454-1#tbox1

"Summary
Cells need to be able to sense different types of signals, such as chemical and mechanical stimuli, from the extracellular environment in order to properly function. Most eukaryotic cells sense these signals in part through a specialized hair-like organelle, the cilium, that extends from the cell body as a sort of antenna. The signaling and sensory functions of cilia are fundamental during the early stages of embryonic development, when cilia coordinate the establishment of the internal left–right asymmetry that is typical of the vertebrate body. Later, cilia continue to be required for the correct development and function of specific tissues and organs, such as the brain, heart, kidney, liver, and pancreas. Sensory cilia allow us to sense the environment that surrounds us; for instance, we see as a result of the connecting cilia of photoreceptors in our retina, we smell through the sensory cilia at the tips of our olfactory neurons, and we hear thanks to the kinocilia of our sensory hair cells. Motile cilia, which themselves have sensory functions, also work as propeller-like extensions that allow us to breathe because they keep our lungs clean, to reproduce because they propel sperm cells, and even to properly reason because they contribute to the flow of cerebrospinal fluid in our brain ventricles. Not surprisingly, defects in the assembly and function of these tiny organelles result in devastating pathologies, collectively known as ciliopathies (Box 1). Thus, the proper function of cilia is fundamental for human health."

From Evolution News:

https://evolutionnews.org/2021/06/cilium-and-intraflagellar-transport-more-irreducibly-...

"Consider first how many players are needed to build a cilium. Pigino’s parts list begins with microtubules in a 9+2 arrangement going up the cilium from base to tip. The two center microtubules are singlets; the outer ring of 9 are in doublet pairs. Riding on those rails are two engines: kinesin-2, which travels from base to tip (anterograde), and dynein-2, which goes from tip back to the base. Kinesin-2 has a head, stalk, hinge and two “feet” (called heads) that walk on the microtubule while carrying a load; the engine contains six protein subunits. Dynein-2 also has a motor, stalk, linker and tail, and is powered by two AAA+ domains that spend ATP for power. Those are the two engine types, and they work in teams along the microtubules.

"IFT proteins are numbered, such as IFT8 and IFT176. IFT complexes, such as IFT-A, is composed of six IFT proteins. IFT-B, with 16 IFT proteins is another complex. These ride along the trains to the tip, acting as adaptors for the cargo, which include tubulin proteins, dynein parts, membrane proteins and other IFT proteins.

"At the base, a basal body structure called the BBSome forms out of eight BB proteins. It functions as the cargo adaptor for the anterograde train. It authenticates other molecules trying to enter the cilium and moves cargo exiting the retrograde train. Overall, “About 24 different proteins constitute the theoretical minimal functional unit of IFT,” Pigino says, although much needs to be learned.

***

"A precise sequence of amino acids is required for each protein’s function, and the longer the protein, the more improbable that chance could get it right. IFT proteins are large. For instance, BBS1 in the BBSome has 593 amino acid residues; IFT172 (part of the IFT-B complex) has 1,749. The improbability is exacerbated when proteins have to work together. It’s not necessary to belabor the point again, but it’s instructive that Pigino never mentions evolution in her article.

"Moving cargo up and down the cilium takes place in five steps. First, the train assembles at the base. Kinesins line up along a microtubule doublet, their “heads” touching the tracks. Parts of dynein (the return engine) are loaded so as not to touch the tracks, avoiding a “tug-of-war” between the engines. Membrane parts and other cargoes are loaded with the help of IFT-A and IFT-B. Like a well-organized monorail car, the completed train “walks” up the track aided by multiple kinesin-2 engines powered by ATP.

"At the tip, the third phase begins. Cargo is unloaded and ferried to the growing cilium (microtubules and membrane). Concurrently, the dynein engines are assembled in an “open configuration as an intermediate state to ensure a controlled activation.” The kinesins are disassembled for transport back to the base. The fourth stage activates the dyneins and starts the train moving, carrying both IFT complexes and waste products to the base. The fifth and final stage unloads the cargo, disassembles the retrograde train and recycles the parts. If you conceive of railcars in a narrow mine shaft carrying tools needed by miners at the far end, and returning the carts with waste products, the analogy seems apt — only the cell’s actions are all automated."

Comment: the study of the bacterial flagellum all over again evolved into helpful celia/hairs that are vital to health. Pure irreducible complexity requiring a designer.