Chaperones Flashcards
What are chaperones?
A diverse family of gene products characterised into families according to their molecular weight whose expression is usually heat induced.
What do sHSP do?
Act as buffers of protein aggregation in heat shock (or other stresses), reversible bind mis folded proteins and prevent aggregation.
Describe Hsp90?
The least well understood HSP. Binds ATP and other proteins and acts on protein conformation, Raf-1 signalling and steroid hormone receptor activation.
Describe hsp100?
Hsp104 in yeast and ClpB in E.coli has a major role in protein disaggregation and degradation.
Describe hsp70?
DNAk in E.coli, 70 kDa monomeric weak ATPase and strong affinity for non native proteins with exposed hydrophobic sequences.
What does hsp70 work with?
Hsp40, DNAJ in E.coli, has no ATPase activity. And nucleotide exchange factor GrpE.
What do type two HSP have?
A built in cap
What is GroEL and GroES equivalent to in eukaryotes?
hsp60/hsp10
Describe GroEL?
800 kDa. 14, 57.4 Da, 549 residue subunits, arranged in two stacked rings. Has a weak ATPase activity and a strong affinity for non-native proteins.
Describe GroES?
Caps GroEL. A dome shaped heptameric ring structure of 97-residue subunits.
What is the height and width of the GroE chaperonin?
184 Å and 140 Å
Describe the reaction cycle the GroE chaperonin uses?
GroEL with 7 ATP and a substrate binds GroES causing a conformational change which hides the hydrophobic residues relapsing the protein into the chamber. It begins to fold into a better conformation and the ATP are hydrolysed. The release of the 7 inorganic phosphates causes a reduction in the affinity of GroES for GroEL. Once hydrolysed the trans ring can guide 7 ATP and a substrate and the previous substrate, now 7 ADP and GroES are released. A 180o rotation starts the cycle again.
Define a chaperone?
A protein that is involved in the correct folding, transport, assembly or degradation of a polypeptide without becoming part of the final functional complex.
