11/27/2008

US-American Researchers Learn How Bleach Kills Bacteria

New research from the US-American University of Michigan reveals key details in
the process by which bleach works its antimicrobial magic. In a study published
in the Nov. 14 issue of the journal Cell, a team led by molecular biologist
Ursula Jakob describes a mechanism by which hypochlorite, the active ingredient
of household bleach, attacks essential bacterial proteins, ultimately killing
the bugs.

"As so often happens in science, we did not set out to address this question,"
said Jakob, an associate professor of molecular, cellular and developmental
biology. "But when we stumbled on the answer midway through a different
project, we were all very excited." Jakob and her team were studying a
bacterial protein known as heat shock protein 33 (Hsp33), which is classified
as a molecular chaperone. The main job of chaperones is to protect proteins
from unfavorable interactions, a function that's particularly important when
cells are under conditions of stress, such as the high temperatures that result
from fever.

"At high temperatures, proteins begin to lose their three-dimensional molecular
structure and start to clump together and form large, insoluble aggregates,
just like when you boil an egg," said lead author Jeannette Winter, who was a
postdoctoral fellow in Jakob's lab. And like eggs, which once boiled never turn
liquid again, aggregated proteins usually remain insoluble, and the stressed
cells eventually die.

Jakob and her research team figured out that bleach and high temperatures have
very similar effects on proteins. Just like heat, the hypochlorite in bleach
causes proteins to lose their structure and form large aggregates.
"Many of the proteins that hypochlorite attacks are essential for bacterial
growth, so inactivating those proteins likely kills the bacteria," said second
author Marianne Ilbert, a postdoctoral fellow in Jakob's lab.

These findings are not only important for understanding how bleach keeps our
kitchen countertops sanitary, but they may lead to insights into how we fight
off bacterial infections. Our own immune cells produce significant amounts of
hypochlorite as a first line of defense to kill invading microorganisms.
Unfortunately, hypochlorite damages not just bacterial cells, but ours as well.
It is the uncontrolled production of hypochlorite acid that is thought to cause
tissue damage at sites of chronic inflammation.

How did studying the protein Hsp33 lead to the bleach discovery? The
researchers learned that hypochlorite, rather than damaging Hsp33 as it does
most proteins, actually revs up the molecular chaperone. When bacteria
encounter the disinfectant, Hsp33 jumps into action to protect bacterial
proteins against bleach-induced aggregation.

"With Hsp33, bacteria have evolved a very clever system that directly senses
the insult, responds to it and increases the bacteria's resistance to bleach,"
Jakob said.


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AplusA-online.de - Source: Environmental Protection