Biological complexity: intramembrane enzyme cuts proteins (Introduction)

by David Turell , Saturday, February 03, 2018, 21:02 (2485 days ago) @ David Turell

A recently found enzyme is hydrophobic and chops up proteins into smaller parts for further use:

https://phys.org/news/2018-02-hatchet-enzyme-enabler-sickness-health.html

"Tucked away inside cell membranes, a molecular butcher does the bidding of healthy cells but also of disease agents. It has been operating out of clear view, but researchers just shined a mighty spotlight on it.

"The butcher is a common enzyme called presenilin, which chops lengthy protein building blocks down to useable shorter lengths. It resides in membrane spaces that evade ready experimental detection.

***

"'One third of our genome goes to work to encode intramembrane proteins," said Raquel Lieberman, an associate professor in Georgia Tech's School of Chemistry and Biochemistry. "Some of them are huge and do super complex biochemistry."

"The enzyme presenilin in particular is an intramembrane protease. There are four classes of these, and they are needed, among other things, for: Alerting to and defending against infectors, and cell differentiation and development.

***

"Presenilin (MmIAP) is armed with two chemical knives, aspartates, that reliably make cuts on peptides, the subunits that make up proteins. And a second new study by the same researchers illuminated how the cleaving works.

"Presenilin can trim peptides into building blocks helpful to its own cells, or whittle bad peptide chunks that end up in amyloid-beta plaque, a suspect in Alzheimer's disease. Or presenilin can aid and abate hepatitis C viruses by carving components it needs to reproduce.

***

"Presenilin and other intramembrane proteins warrant such proverbial desperate measures. They live in a lipid environment and hate water about the way cats do, and that's a problem for researchers studying them.

"'When you have proteins that are not soluble in water, you're in trouble," Lieberman said. "The usual techniques to analyze them become very, very difficult, if not impossible. And when you chemically bootstrap these proteins to be able use these water-soluble methods, you have really poor chances of seeing the protein's actual structure that performs its function.'"

Comment: Another addition to cell complexity. Enzymes are giant molecules. A chance mechanism of evolution could never design a hydrophobic molecule of this size and complexity. It has to do its work inside the lipids of the cell membrane walls, where water is not used as a solute, while most of life is very wet with water. Our bodies are about 90% water.