abnormal interactions with many cellular
proteins (10). The normal structure of the fibrils contains these dangerous
surfaces, this explaining why the soluble oligomers are much more interactive
than fibrils.  However, the fibril contributes to pathology
by both generating oligomers through fragmentation and secondary nucleation and
by stably sequestering key cellular factors (12, 13). The
metastable proteins are often targeted by toxic aggregates; they are present
at the unstructured regions and low amino acid complex, can distinguish many
RNA-binding proteins (9,13). Accordingly, There is an interferes between protein
aggregation with nucleocytoplasmic RNA transport and RNA homeostasis (6,11). Many studies have proven that the protein
degradation can inhibited by the aggregates proteasome and autophagy systems (6) and can isolate chaperone components(4,13).
Proteostasis decline and symptom as a result
of interferes between aggregation with protein quality control. Aggregate is essential to determine cell
viability and the life span of model organisms. Recent study by Frydman and colleagues (10),
noted that there is difference between protein aggregation in the cell and
aggregation in vitro which mean that cells contain complex mechanisms that
involve particular chaperon proteins, for instance the small heat shock protein
Hsp42 (6), have been developed to minimize the toxic effects exerted by soluble
oligomers (8). Actively sequester surplus and misfolded proteins into transient
or stable deposits when their timely degradation fails. These mechanisms, which
involve specific chaperone proteins like the small heat shock protein Hsp42 (7),
have apparently evolved to reduce the toxic effects exerted by soluble
oligomers (13). These compartments include the insoluble
protein deposit (IPOD) which discovered in the yeast cells (12). The IPOD terminates
the toxic amyloid and prion proteins in the cell periphery near the vacuole (8)
this equivalent to the mammalian cells aggresome as a site of aggregate
sequestration (11).  In the transient sequestration the
compartments are called Q-bodies and the juxtanuclear quality control
compartment (JUNQ) (4). The Q-bodies present immediately when protein
misfolding, for instance, under stress they concentrate in the JUNQ in case of degradation,
for instance, under stress they concentrate in the JUNQ in case of degradation
if the ubiquitin proteasome system failsOther misfolded proteins is cytosolic, potentially
routed to an intranuclear quality control compartment (INQ) (7), which play
pivotal role in degradation of cytosolic proteins and quality control (3, 11).

In conclusion, the massive development that
has been made in last few years in terms of discovering the structure of
pathological protein aggregates and their mechanisms of toxicity. Together with
explaining the relationship between the effective proteostasis network and misfolded
proteins, to find way to prolong the healthy life span.   


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