Exchangeable chaperone modules contribute to specification of type I and type II Hsp40 cellular function

Area of Science:

• Molecular Biology
• Protein Folding
• Cellular Physiology

Background:

• Hsp40 proteins regulate Hsp70 chaperones, which are crucial for protein folding and cellular functions.
• Yeast Hsp40s, Ydj1 and Sis1, pair with Hsp70 Ssa1, but the mechanism for their distinct functions is unclear.
• Both Ydj1 and Sis1 possess unique central protein modules implicated in their chaperone activity.

Purpose of the Study:

• To investigate whether the central chaperone modules of Ydj1 and Sis1 determine Hsp70 action specificity.
• To construct and analyze chimeric Hsp40 proteins with swapped chaperone domains.

Main Methods:

• Construction of chimeric Hsp40s (YSY and SYS) by swapping Ydj1 and Sis1 chaperone domains.
• In vitro analysis of protein-folding activity and substrate specificity of chimeric Hsp40s.
• In vivo studies to assess the functional complementation of lethal phenotypes and prion maintenance.

Main Results:

• Purified SYS and YSY exhibited protein-folding activities and substrate specificities mirroring Ydj1 and Sis1, respectively.
• In vivo, the YSY chimera showed a gain of function, complementing the lethal phenotype of sis1 Delta.
• YSY facilitated the maintenance of the prion [RNQ+], a function not observed with Ydj1.

Conclusions:

• The chaperone modules of Ydj1 and Sis1 are exchangeable and play a key role in specifying Hsp70 functions.
• Chimeric Hsp40s demonstrate that these modules dictate distinct cellular roles and substrate specificities.
• This finding provides insight into the modular nature of chaperone regulation and function.