Partial dispensability of Djp1's J domain in peroxisomal protein import in Saccharomyces cerevisiae results from genetic redundancy with another class II J protein, Caj1

Abstract

J proteins are obligate co-chaperones of Hsp70s. Via their signature J domain, all J proteins interact with their partner Hsp70s and stimulate their weak ATPase activity, which is vital for Hsp70 functions. The dependency of J proteins on their J domain is such that mutations in critical amino acids in the J domain often results into a null phenotype for a particular J protein. Here, we show that the J domain of Djp1, a cytosolic J protein important for peroxisomal protein import in Saccharomyces cerevisiae, is partially dispensable. A complete deletion of Djp1 J domain resulted into only partial loss in peroxisomal protein import function. Instead, the C-terminal domain of Djp1 was found to be essential for proper localization of the peroxisomal targeted GFP-PTS1. Furthermore, we show that Caj1, another cytosolic J protein, also has some role in peroxisomal protein import. Caj1 was found to be partially redundant with Djp1 as cells lacking both Djp1 and Caj1 resulted into a much more severe defect in GFP-PTS1 localization. Based on these results, we propose that dispensability of J domains could be attributed to genetic redundancy between different J proteins sharing common structural topology and cellular localization.

Nanodisc-Based Proteomics Identify Caj1 as an Hsp40 with Affinity for Phosphatidic Acid Lipids

“…Next, we attempted to identify residues within Caj1 that may be responsible for mediating its interaction with PA. Since the N-terminal 80 residues of Caj1 constitute the conserved J-domain, we confined our search to the more variable C-terminal portion of the protein. , For the few other characterized PA-interacting proteins, PA recognition is mediated through short clusters of positively charged residues, often lysine or arginine. ,, Examination of the sequence of Caj1 (, accessed April 23, 2021) reveals two double lysine motifs: KK 245–246 and KK 335–336. For clarity, we term KK 245–246 “Patch 1” and KK 335–336 “Patch 2” (Figure A).…”

“…Since the N-terminal 80 residues of Caj1 constitute the conserved Jdomain, we confined our search to the more variable Cterminal portion of the protein. 27,32 For the few other characterized PA-interacting proteins, PA recognition is mediated through short clusters of positively charged residues, often lysine or arginine. 3,6,9 Examination of the sequence of Caj1 (https://www.uniprot.org/uniprot/P39101, accessed April 23, 2021) reveals two double lysine motifs: KK 245− 246 and KK 335−336.…”

Nanodiscs-based proteomics identify Caj1 as an Hsp40 with affinity for phosphatidic acid lipids

“…Next, we attempted to identify residues within Caj1 that may be responsible for mediating its interaction with PA. Since the N-terminal 80 residues of Caj1 constitute the conserved J-domain, we confined our search to the more variable C-terminal portion of the protein 26, 28 . For the few other characterized PA-interacting proteins, PA recognition is mediated through short clusters of positively charged residues – often lysine or arginine 3, 6, 9 .…”

Targeting and translocation of proteins to the endoplasmic reticulum at a glance

“…Additionally, Pex5 has been suggested to act in a PTS1-independent manner, which may explain the peroxisomal import of some proteins that lack a PTS (van der Klei and Veenhuis, 2006). Additional cytosolic factors are emerging as facilitators of protein import into peroxisomes, with the HSP40 Djp1 (Dobriyal et al, 2017;Hettema et al, 1998) and calmodulin (Corpas and Barroso, 2017) among them.…”