Healthcare and Medicine Reference
In-Depth Information
REMOVAL OF OXIDIZED PROTEINS
As described in Chapter 1 the protein pool is exposed to a continuous influ-
ence of metabolic and environmental damaging agents, leading to a permanent
formation of proteins oxidized, modified, unfolded, or otherwise disrupted in
their structure and functionality. In order to maintain the cellular functionality
and viability, it is important that such nonfunctional proteins undergo either
repair or defined turnover. In order to realize this, damaged, modified, and
misfolded proteins, or proteins that have become unnecessary, must be recog-
nized selectively in a first step and afterward, in a second step, either repaired
or degraded. During evolution several systems have developed for this purpose,
including a number of repair systems, as well as cellular protein turnover
mechanisms which are able to degrade oxidized proteins. It is therefore pro-
posed that a complex interaction of repair, folding, and degradation mecha-
nism enables the cell to maintain a functional protein pool during lifetime.
Interestingly, the folding and degradation mechanisms have multiple functions
in the cell, which are far beyond the selective removal of oxidized proteins.
The main mechanism enabling cells to repair or remove oxidized proteins
will be introduced in this chapter. These include the repair mechanisms for
sulfur-containing amino acids; the protein removal systems, including the
proteasomal system; the lysosomal cathepsins; the Lon protease; and, to
some extent, the role of chaperones in the context of solubilizing oxidized
proteins.
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