Biological complexity: cell 'water wires' pass info (Introduction)

by David Turell , Wednesday, July 29, 2020, 23:59 (1578 days ago) @ David Turell

One molecule wide channels pass ions:

https://evolutionnews.org/2020/07/biophysicists-find-water-wires-are-biological-informa...

"Water conducts electricity; it can also conduct energy and information. Biophysicists are finding that “water wires” at the nanoscale fine-tune enzymatic actions — indeed, can be indispensable for function.

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"Cells need to both attract the right molecules to go through the channel and authenticate them through the “selectivity filter.” Water can assist this process via electricity. Since H2O is bipolar, single water molecules in a chain, held together by hydrogen bonds, become a sort of “wire” through which ions can pass. Additionally, the fact that some amino acids are hydrophilic allows biological channels to attract water molecules to the exact positions inside the channel where they can assist the selectivity filter.

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"Water wires are critical for the functioning of many membrane proteins, as in channels that conduct water, protons, and other ions. Here, in liquid crystalline lipid bilayers under symmetric environmental conditions, the selective hydrogen bonding interactions between eight waters comprising a water wire and a subset of 26 carbonyl oxygens lining the antiparallel dimeric gramicidin A channel are characterized by 17O NMR spectroscopy at 35.2 T … and computational studies.

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"The results reveal that selective pore-lining carbonyl oxygens form remarkably stable hydrogen bonds with waters in the wire, such that the water wire does not change its orientation on the millisecond NMR timescale. The stable orientation of the water-wire dipole also provides a simple explanation for the low affinity of the second cation binding site in this dimeric channel, despite a separation of ∼24 Å from the first binding site at the opposite end of the pore.

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"The water wire itself has a stability gradient from the negative end of the electric dipole to the positive end, based on optimal hydrogen bonding of the waters at the negative end of the electric dipole. The water interactions at this end of the dipole over the first three waters of the water wire are particularly stable.

"Is there a reason why the hydrogen bonds need to be stable? Yes; the timing of passage of cations requires that the binding sites not flip too quickly.

"Water wires are critical biological assemblies supported by membrane proteins for the purposes of transporting charge and ions across membranes.

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"In short, the spacing of all the amino acids and water molecules is optimized for function. The first ion is sucked in, forming its stable hydrogen bonds with the water, so that the second ion entering the channel doesn’t flip the dipole over and break the flow. That requires precision foresight both positionally and temporally. And this is one of the simplest examples found in a bacterium! It is fair to expect even more optimization will be found in future studies of water wires in more complex membrane channels.

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"The profound influence of the water wire in this model system and the stable water–carbonyl interactions illustrate the significance and functionality for such wires in many channels and materials. In particular, the stability of the water wire and its electric dipole suggests that its influence in many other systems could be more significant than generally recognized. To achieve such an understanding, unique 17O spectroscopy as reported here at a field strength of 35.2 T demonstrates the exquisite sensitivity to the chemical environs surrounding oxygen sites where so much of biological chemistry takes place."

Comment: This is why water must be present for life to appear. An amazingly designed system, not by chance. The source article is extremely complex:

https://www.pnas.org/content/117/22/11908.full

The abstract first sentence: "Water wires are critical for the functioning of many membrane proteins, as in channels that conduct water, protons, and other ions. Here, in liquid crystalline lipid bilayers under symmetric environmental conditions, the selective hydrogen bonding interactions between eight waters comprising a water wire and a subset of 26 carbonyl oxygens lining the antiparallel dimeric gramicidin A channel are characterized by 17O NMR spectroscopy at 35.2 T (or 1,500 MHz for 1H) and computational studies." "Nuff said.