Biology subjects

Li, Z. J.

Publications and source records attributed to Li, Z. J..

3 recordsLinked to original sources

bioRxiv2025

Functional integrity of the SEL1L-HRD1 complex is critical for ERAD and organismal viability

The SEL1L-HRD1 complex represents the most evolutionarily conserved branch of endoplasmic reticulum-associated degradation (ERAD), with SEL1L acting as a key cofactor for the E3 ubiquitin ligase HRD1. While the physiological relevance of this complex has been increasingly recognized, whether SEL1L is strictly required for HRD1 function in mammals has remained unclear. Here, using complementary in vivo and in vitro approaches, we define the architecture and physiological significance of the mammalian SEL1L-HRD1 ERAD complex. Our data demonstrate that direct binding between SEL1L and HRD1 is essential for ERAD function and neonatal survival in mice. In three knock-in mouse models harboring targeted mutations at the SEL1L-HRD1 interface, we show that the L709P variant - unlike the benign P699T mutation - results in complete neonatal lethality within 30 hours of birth, a phenotype more severe than that of the partially lethal S658P variant. Mechanistically, the L709P mutation abolishes SEL1L-HRD1 interaction, disrupting substrate engagement and impairing recruitment of the E2 enzyme UBE2J1, leading to the accumulation and aggregation of misfolded proteins in the ER. Notably, these defects can be partially rescued by HRD1 overexpression, echoing findings from yeast. Together, our results provide definitive evidence that the SEL1L-HRD1 interaction is essential for ERAD activity and neonatal viability in mammals, resolving a long-standing question in ERAD biology and identifying a new therapeutic strategy for modulating ERAD activity in humans. SIGNIFICANCE STATEMENTThe endoplasmic reticulum-associated degradation (ERAD) pathway is essential for maintaining cellular proteostasis and organismal health, yet its molecular regulation in mammals remains incompletely defined. The SEL1L-HRD1 complex constitutes the central axis of this conserved pathway, but whether SEL1L is required for HRD1 function in vivo has remained unresolved. Here, using genetic mouse models and biochemical analyses, we demonstrate that the physical interaction between SEL1L and HRD1 is essential for ERAD activity and neonatal viability. These findings resolve a long-standing question in ERAD biology, provide new insights into the structural and functional organization of the mammalian ERAD machinery, and highlight the SEL1L-HRD1 interface as a potential therapeutic target for modulating ERAD activity in diseases.

cell biology↗

bioRxiv2025

A molecular switch in NAC prevents mitochondrial protein mistargeting by SRP

The nascent polypeptide-associated complex (NAC) co-translationally screens all nascent proteins and regulates their access to the signal recognition particle (SRP) to ensure the fidelity of protein targeting to the endoplasmic reticulum (ER). However, the mechanism by which NAC prevents the mistargeting of nascent mitochondrial proteins remains unclear. Here, we identified a molecular switch in NAC that allows its central barrel domain to adopt a stabilized conformation on ribosomes exposing a mitochondrial targeting sequence (MTS). Mutations of the MTS on the nascent chain or in the NAC switch region increases NAC barrel dynamics and reduces its binding to the ribosome. This leads to an impaired ability of NAC to prevent mistargeting by SRP and causes ER stress in human cells. Our work reveals how NAC detects nascent mitochondrial proteins early in translation and prevents their promiscuous access to SRP, elucidating the structural basis that underlies this role and providing novel insights into protein targeting fidelity with broader implications for cellular proteostasis.

biophysics↗

bioRxiv2023

SEL1L-HRD1 ER-associated degradation is a new ataxia gene

The SEL1L-HRD1 protein complex represents the most conserved branch of endoplasmic reticulum (ER)-associated degradation (ERAD); however, definitive evidence for the importance of SEL1L in HRD1 ERAD is lacking. Here we report that attenuation of the interaction between SEL1L and HRD1 impairs HRD1 ERAD function and has pathological consequences in mice. Our data show that SEL1L variant p.Ser658Pro (SEL1LS658P) previously identified in Finnish Hound suffering cerebellar ataxia is a recessive hypomorphic mutation, causing partial embryonic lethality, developmental delay, and early-onset cerebellar ataxia in homozygous mice carrying the bi-allelic variant. Mechanistically, SEL1LS658P variant attenuates the SEL1L-HRD1 interaction and causes HRD1 dysfunction by generating electrostatic repulsion between SEL1L F668 and HRD1 Y30 residues. Proteomic screens of SEL1L and HRD1 interactomes revealed that the SEL1L-HRD1 interaction is prerequisite for the formation of a functional HRD1 ERAD complex, as SEL1L recruits not only the lectins OS9 and ERLEC1, but the E2 UBE2J1 and retrotranslocon DERLIN, to HRD1. These data underscore the pathophysiological importance and disease relevance of the SEL1L-HRD1 complex, and identify a key step in organizing the HRD1 ERAD complex.

cell biology↗