# Structural Analysis of Human LonP1 Protease Bound with the Native Substrate

## TL;DR

This study reveals how the human LonP1 protease recognizes and degrades its native substrate, providing insights into mitochondrial function and disease.

## Contribution

The paper presents the first high-resolution cryo-EM structure of human LonP1 bound to its native substrate, TFAM.

## Key findings

- The human LonP1 hexamer uses a bipartite search-and-shred mechanism to process substrates.
- The N-terminal domain acts as a selective vestibule for substrate recruitment and unfolding.
- A hand-over-hand threading mechanism is driven by aromatic pore-loops in the central channel.

## Abstract

The human mitochondrial Lon protease (LonP1) is a central regulator of mitochondrial DNA copy number and metabolic reprogramming. However, the structural basis for how LonP1 recognizes native physiological substrates remains elusive. Here, we present the high-resolution cryo-EM structure of the human LonP1 hexamer actively engaging its native substrate, TFAM. The reconstruction reveals a distinct bipartite search-and-shred mechanism. Unlike its bacterial homologs, the human N-terminal domain (NTD) adopts a compact architecture acting as a selective vestibule to recruit and initially unfold the substrate tertiary structure. Subsequently, the polypeptide is threaded through the central channel via a hand-over-hand mechanism driven by a spiral array of aromatic pore-loops. This structural framework provides a mechanistic rationale for the spatial segregation of LonP1 and offers a template for targeting mitochondrial proteostasis in human diseases.