Synthetic lethal interactions in yeast reveal functional roles of J protein co-chaperones

Abstract

J proteins are a diverse family of co-chaperones that cooperate with heat shock protein 70 (Hsp70) to coordinate protein quality control, especially in response to cellular stress. Current models suggest that individual J proteins might play roles in recruiting Hsp70s to specific functions, such as maintaining cell wall integrity or promoting ribosome biogenesis. However, relatively few stresses have been used to test this model and, as a result, only a few specific activities have been identified. To expand our understanding of the J protein network, we used a synthetic lethal approach in which 11 Saccharomyces cerevisiae deletion strains were treated with 12 well-characterized chemical inhibitors. The results defined new roles for specific J proteins in major signaling pathways. For example, an important role for Swa2 in cell wall integrity was identified and activities of the under-explored Jjj1, Apj1, Jjj3 and Caj1 proteins were suggested. More generally, these findings support a model in which some J proteins, such as Ydj1 and Zuo1, play “generalist” roles, while others, such as Apj1 and Jjj2, are “specialists”, having roles in relatively few pathways. Together, these results provide new insight into the network of J proteins.

A Putative Biochemical Engram of Long-Term Memory

“…In a reciprocal screen we overexpressed 57 out of 63 individual yeast chaperones by a galactose-inducible system (Fig 4B & S3). Both the deletion and overexpression screen consistently identified JJJ2, a lowly expressed (~200 molecules/cell, Yeast Genome Database) DNA-J domain containing protein in Hsp40 family [45, 46] that surprisingly facilitates the aggregation of Orb2AprD-Sup35C protein. When Orb2AprD-Sup35C is in the aggregated (prion-like) state, cells are white and can grow in media lacking adenine and in non-aggregated state cells are red and can’t grow in media lacking adenine.…”

Variant‐specific and reciprocal Hsp40 functions in Hsp104‐mediated prion elimination

“…This newly uncovered Apj1 function required both a functional J‐domain and C‐terminal peptide binding domain, indicating that Apj1 likely acts through Hsp70 in this process and that client‐protein binding is likely important. Apj1 is localized in mitochondria to a greater extent than other J‐proteins (Ghaemmaghami et al ., ), and with an estimated 100 copies per cell, Apj1 is also the least abundant cytosolic J‐protein, especially relative to 90,000 copies per cell of Ydj1 (Ghaemmaghami et al ., ; Gillies et al ., ; Sahi et al ., ). Yet despite these gross differences in expression level and localization, overexpression of Ydj1 was incapable of compensating this SUMO‐related functionality of Apj1 (Sahi et al ., ), which aligns with our observations here regarding Hsp104 curing.…”

Chaotropicity: a key factor in product tolerance of biofuel-producing microorganisms

“…The highest concentration of butanol achieved in conventional batch fermentation to date was approximately 2.1% (w/v), which was obtained by using C. beijerinkii BA101 generated by nitrosoguanidine (NTG) mutagenesis and supplementing the growth medium with acetate [182] A further study which also analysed traits of hybrid S. cerevisiae strains revealed a relationship between ethanol tolerance and lower expression levels of APJ1, a gene which encodes for a mitochondrial cochaperone that binds to Hsp70 molecules [113 ]. APJ1 is a 'specialist' chaperone that targets specific proteins which, presumably, are non-essential for ethanol tolerance [196]. The absence of APJ1 protein, therefore, leaves more Hsp70 subunits available to protect proteins that are more essential and are involved in ethanol stress-tolerance.…”