Project Details
Projekt
Nuclear quality control of non-imported mitochondrial precursor proteins
Applicants
Dr. Fabian den Brave; Privatdozent Dr. Axel Mogk
Subject Area
Biochemistry
Term
since 2024
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 541596792
Impairment or overload of mitochondrial import lead to the accumulation of mitochondrial precursor proteins (mitoPREs), which are prone to misfolding and aggregation. mitoPREs can be targeted to the nucleus for protein quality control (PQC), though the diverse nuclear proteostasis strategies and their physiological relevance remain poorly understood. We will define the role of the nucleus as important PQC hub for mitoPREs using Saccharomyces cerevisiae as model system. We will put a special emphasis on the nuclear J-domain protein (JDP) Apj1, which functions as Hsp70 co-chaperone. We show that (i) Apj1 binds to mitoPREs and (ii) apj1 mutant cells show specific growth defects on respiratory growth medium (YPG) and upon expression of a clogger-construct blocking mitochondrial protein import, underlining the relevance of Apj1 for mitochondrial function. Furthermore, we show strong negative genetic interactions of Apj1 with Ydj1, the major cytosolic JDP, on respiratory but not on fermentative growth medium. apj1 ydj1 mutants hardly grow on YPG and display reduced levels of respiratory chain subunits, suggesting general defects in mitochondrial biogenesis and overlapping functions of both JDPs. We finally show that Apj1 is a negative regulator of the heat shock response by specifically repressing Hsf1 activity. This offers the possibility for directly adjusting chaperone gene expression to the accumulation of mitoPREs in the nucleus via Apj1. Together our findings indicate a central role of nuclear Apj1 in sensing and handling mitoPREs. We plan to: (1) Dissect the role of the nucleus as general hub for mitoPREs by identifying the nuclear import machinery through a genetic screen and determining the consequences on mitoPRE destiny and cytosolic PQC upon abolishing nuclear import. (2) Determine the complete mitoPRE substrate pool of Apj1 and the role of Apj1 in mitoPRE handling by using identified native substrates as reporters. We will additionally dissect the functional interplay of Apj1 with other nuclear PQC activities such as protein sequestration and proteasomal degradation and its functional overlap with Ydj1 in maintaining mitochondrial integrity. (3) Determine the mechanism of Apj1 through rigid structure-function analysis and to reconstitute Apj1 activity in vitro. Here, we will additionally study the ability of Apj1 to bind SUMO, pointing to a specific way of substrate recognition and downstream processing. (4) Analyze the potential role of Apj1 as mediator linking the nuclear accumulation of mitoPREs to the activation of the Hsf1-dependent stress response.
DFG Programme
Priority Programmes
