Completing the Protein life cycle Flashcards
proteins begin to fold even before
their synthesis by is completed
ribosomes
is a very crowded place, with
effective protein concentrations as
high as Blank
cytosolic environment, 0.3 g/mL
enhances the likelihood of
nonspecific protein association and aggregation
macromolecular crowding
the primary driving force for
protein folding is the burial of
Blank away from the aqueous solvent and reduction in solvent-accessible surface area
hydrophobic side chains
the folded protein typically has a
buried Blank core and a blank
surface
Hydrophobic, Hydrophilic
is driven by hydrophobic interactions, so burial
of hydrophobic regions through
folding is a crucial factor in
preventing aggregation
protein aggregation
to evade aggregation, nascent
proteins are often assisted in folding by a family of helper proteins known as Blank
molecular chaperone
- abundant proteins in cells given
brief exposure to high temperature
(42°C)
Heat shock proteins (Hsps)
fold efficiently without the aid of
chaperones
small, single-domain proteins
proteins often require chaperones,
especially in the crowded milieu of a cell
larger proteins and multi-domain
protein folding by chaperones is
often Blank
ATP-dependent
- bind to the chaperone complex and control ATP hydrolysis activity and protein folding
cochaperones
in E. coli, the Blank ribosomal protein Blank, which is situated at the peptide exit tunnel, serves as the docking site for TF, directly linking protein synthesis with chaperone-assisted
protein folding
50S ribosomal protein L23
Bind to Hydrophobic Regions of Extended Polypeptides
Hsp70 Chaperones
- the principal Hsp70 in E. coli
- recognizes exposed, extended regions of polypeptides that are rich in hydrophobic residues
DnaK
is energy-dependent and is
driven by ATP hydrolysis
release
a Blank that binds polypeptides with exposed hydrophobic regions
18-kDa central domain
Blank constitutes 1% to 2% of the
total cytosolic proteins of
eukaryotes, its abundance reflecting its importance
Hsp90
- chaperonins
- assists some partially folded
proteins (10% of the cytosolic
proteome) to complete folding after
their release from ribosomes
Hsp60 class of chaperones
- found in bacteria
Group I chaperonins
- found in archaea and eukaryotes
Group II
- group I chaperonin in E. coli
GroES–GroEL complex
- made of 2 stacked 7-membered
rings of 60 kDa subunits that form a cylindrical 14 oligomer 15 nm high
and 14 nm wide
GroEL
- co-chaperonin
- consists of a single 7-membered
ring of 10 kDa subunits that sits like a dome on one end of GroEL (apical
end)
GroES
