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.