# Molecular insights on the mechanism of α1-antitrypsin condensate formation and maturation

## TL;DR

This study uses simulations to show how a faulty protein forms harmful clumps in cells, offering new insights into a genetic disorder that causes liver and lung disease.

## Contribution

The study reveals a novel mechanism of α1-antitrypsin condensate formation involving phase-separated liquid-like droplets driven by the disordered C-terminus of the misfolded variant.

## Key findings

- Misfolded Z-α1-antitrypsin forms liquid-like droplets that harden into solid clusters through β-sheet transitions.
- The native M-α1-antitrypsin has a much lower tendency to phase-separate and form aggregates.
- Z-α1-antitrypsin condensates form more readily near surfaces, mimicking conditions in the endoplasmic reticulum.

## Abstract

The deficiency of α1-antitrypsin protein is a genetic disorder characterized by the accumulation of misfolded protein aggregates within hepatocytes, leading to liver dysfunction. In the lung, it is found in macrophages, bronchial and epithelial alveolar cells type 2, leading to pulmonary emphysema. Despite extensive research, the precise mechanism underlying the formation of α1-antitrypsin inclusion bodies remain elusive. In this study, we combine equilibrium and non-equilibrium molecular dynamics simulations to elucidate the intricate process of α1-antitrypsin condensate formation and maturation. Our mechanistic model explains cluster accumulation—specifically the onset of this pathogenesis—through the emergence of phase-separated liquid-like protein droplets, which subsequently undergo inter-protein β-sheet transitions between misfolded variants, resulting in solid-like clusters. We find that this mechanism only applies to the misfolded variant, Z-α1-antitrypsin, which phase-separates driven by its disordered C-terminus. In contrast, the native protein, M-α1-antitrypsin, shows much lower propensity to phase-separate and later form kinetically trapped aggregates. Furthermore, we explore how Z-α1-antitrypsin exhibits an increased capacity to form condensates near external walls with different types of interactions. Such conditions can be similar to those found within the endoplasmic reticulum membrane, where phase separation and hardening take place. Overall, our results shed light on the molecular basis of α1-antitrypsin-related disorders and provide valuable microscopic insights for the development of therapeutic strategies targeting protein misfolding and aggregation-related disorders.

Alpha-1 antitrypsin deficiency is a genetic disorder that can cause liver and lung disease. It occurs when the protein α1-antitrypsin folds incorrectly and accumulates in harmful clumps inside cells. Exactly how these clumps form has been unclear. In this study, we used computer simulations to reveal the steps behind this process. We found that the faulty version of the protein first collects into liquid-like droplets that later harden into solid clusters. This behavior is driven by a flexible tail region of the misfolded protein. In contrast, the normal version is far less likely to clump. Our findings provide new insight into disease onset and may guide the development of therapies.