Gunjan Mehta, VSC, Rajkot
Gunjan Mehta, VSC, Rajkot
Chaperones: Variations on a theme
DnaJ (Hsp40) Binds folding and misfolded proteins Contains a 30aa glycine-rich region ('G'
domain'), a central Zn binding domain containing 4 repeats of a CXXCXGXG ('CRR' domain) and a C-terminal region of 120 to 170 residues
Associates with DnaK Discovered as requirement for viral
replication
DnaJ hydrophobic = yellowcharged = blue
DnaK (Hsp70) Binds folding and
misfolded proteins Associates with DnaJ ATP binding and
hydrolysis ER homologue Grp78 The interaction of DnaK-
ATP to substrate proteins is transient and characterized by high on/off rates
2 domains alpha helix beta sheet:peptide binding
dnaJ, dnaK, grpE (foldosome)
Cytoplasmic (ER homologues)
Interaction between the J-domain of DnaJ and the N-terminal ATPase domain of DnaK stimulates ATP hydrolysis.
A second interaction mediated by zinc center II locks DnaK on substrate.
The nucleotide exchange factor GrpE then exchanges ADP with ATP and unlocks DnaK.
GroEL (hsp60) Chaperonin
7-fold symmetry
two rings
GroEL (Hsp60)
GroEL
GroEL/GroES complex
GroEl/GroES complex
•Free GroEL binds denatured proteins very tightly.• GroEL undergoes an allosteric transition from its tight-binding state to a weaker binding state on the cooperative binding of nucleotides (ATP/ADP) and GroES. • GroES modulates binding of GroEL•7 ATP molecules bind to GroEL• ATP hydrolysis drives transition back to tight binding state
Hsp90 Abundant 2-3%
eukaryotic cytoplasmic protein (also nuclear)
ER homologue grp94 glycoprotein folding
ATP binding and hydrolysis in both N- and C-terminal domains
Required for protein folding
Prevents protein aggregates
Deletion embryo lethal
ADP
Hsp90 N-terminal domain
Ch
aperon
es in p
rotein fold
ing
Chaperonins in protein folding
Peptide prolyl cis-trans isomerase (PPI) catalyzes the interconversionof the cis and trans isomers of Pro peptide bonds (Fig. 4–8b), which can be a slow step in the folding of proteins that contain some Pro residue peptide bonds in the cis conformation.
Protein disulfide isomerase (PDI) is a widely distributed enzyme that catalyzes the interchange or shuffling of disulfide bonds until the bonds of the native conformation are formed. Among its functions, PDI catalyzes the elimination of folding intermediates with inappropriate disulfide cross-links.