Functional Diversity of Human Mitochondrial J-proteins Is Independent of Their Association with the Inner Membrane Presequence Translocase

Abstract

Mitochondrial J-proteins play a critical role in governing Hsp70 activity and, hence, are essential for organellar protein translocation and folding. In contrast to yeast, which has a single J-protein Pam18, humans involve two J-proteins, DnaJC15 and DnaJC19, associated with contrasting cellular phenotype, to transport proteins into the mitochondria. Mutation in DnaJC19 results in dilated cardiomyopathy and ataxia syndrome, whereas expression of DnaJC15 regulates the response of cancer cells to chemotherapy. In the present study we have comparatively assessed the biochemical properties of the J-protein paralogs in relation to their association with the import channel. Both DnaJC15 and DnaJC19 formed two distinct subcomplexes with Magmas at the import channel. Knockdown analysis suggested an essential role for Magmas and DnaJC19 in organellar protein translocation and mitochondria biogenesis, whereas DnaJC15 had dispensable supportive function. The J-proteins were found to have equal affinity for Magmas and could stimulate mitochondrial Hsp70 ATPase activity by equivalent levels. Interestingly, we observed that DnaJC15 exhibits bifunctional properties. At the translocation channel, it involves conserved interactions and mechanism to translocate the precursors into mitochondria. In addition to protein transport, DnaJC15 also showed a dual role in yeast where its expression elicited enhanced sensitivity of cells to cisplatin that required the presence of a functional J-domain. The amount of DnaJC15 expressed in the cell was directly proportional to the sensitivity of cells. Our analysis indicates that the differential cellular phenotype displayed by human mitochondrial J-proteins is independent of their activity and association with Magmas at the translocation channel.In eukaryotic cells mitochondria form an essential organelle that plays a central role in cancer, apoptosis, and cytotoxic responses and maintains the overall metabolic homeostasis within the cell (1, 2). More than 98% of the human mitochondrial protein pool is nuclear-encoded and transported into the mitochondria through highly complex import machinery spanning the outer membrane, inner membrane, and the intermembrane space (2, 3). At the inner membrane, TIM23 complex forms the sole gateway for translocation of precursor proteins into the matrix, which accounts for ϳ60% of the total imported proteins (4, 5). The TIM23 complex comprises of two components: membrane-embedded Tim23 core channel and the motor component. Although the initial membrane potential dependent translocation is mediated by the Tim23-Tim17 channel, it is the overall activity of the import motor, which determines the translocation process (3, 4, 6 -10). The import motor contains mtHsp70 as its core, whose function is orchestrated by J-proteins (7,(11)(12)(13). The ADP/ATP states of Hsp70 regulate its interactions with client proteins (14, 15). However, the basal ATPase activity of Hsp70 is not sufficient to drive the reactions efficiently and, thus, requires J-proteins as cofactors ...

Tim17 Updates: A Comprehensive Review of an Ancient Mitochondrial Protein Translocator

“…These Pam components also make direct contact with Tim17 and Tim23 and regulate protein translocation. Similar Pam proteins have been found in plants and mammalian systems [29,57] (Table 2). Human DnaJC19 and DnaJC15 are the homologues for Pam18 of yeast.…”

Post Genomics Identification of Blood Stage Invasins of Plasmodium Falciparum

“…JC15 could also efficiently import the precursor proteins in yeast mitochondria in absence of Pam18. The overlapping function of JC15 and Pam18 is probably due to their higher sequence complementarily and similar domain organization (Sinha et al, 2016). This indicates that JC15 is evolutionary more closely related to Pam18.…”

“…This indicates that JC15 is evolutionary more closely related to Pam18. In contrast, JC19 lacks the ability to rescue the viability "pam18 yeast cells which can probably be due to the absence of the region corresponding to Pam18's Nterminal region, in JC19 (Sinha et al, 2016). Since, Jprotein function is primarily implicated to a functional J-domain; it is intriguing why JC19 is unable to functionally complement Pam18.…”

“…In contrast to yeast, which consists of a single J-protein Pam18 as a part of the TIM23 complex (Truscott et al, 2003), human mitochondria is quite unique in expressing two J-proteins, namely JC19 and JC15, as a part of the inner membrane translocation machineries. Both the J-protein paralogs are involved in formation of two mutually distinct and functionally independent subcomplexes with their common J-like protein counterpart Magmas, in comparison to a single Pam16-Pam18 sub complex in yeast (Sinha et al, 2016; (Fig. 1).…”

Mitochondrial diseases: expanding the diagnosis in the era of genetic testing

“…The gene product of DNAJC19 is complexed with another set of proteins, prohibitins, that form protein and lipid scaffolds in the inner mitochondrial membrane. DNAJC19 complex is also involved in protein translocation [200] . The exact role of DNAJC19 is not fully characterized in humans, but pathological variants have been found to induce a phenotype of cardiomyopathy and ataxia, similar to Barth syndrome [201] .…”