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PMEL Amyloid Fibril Formation: The Bright Steps of Pigmentation
Christin Bissig1,2, Leila Rochin3, Guillaume van Niel4,5
1Institut Curie, Paris Sciences et Lettres Research University, UMR144, Centre de Recherche, 26 rue d'ULM, Paris F-75231, France. christin.bissig@curie.fr.
Abstract:
In pigment cells, melanin synthesis takes place in specialized organelles, called melanosomes. The biogenesis and maturation of melanosomes is initiated by an unpigmented step that takes place prior to the initiation of melanin synthesis and leads to the formation of luminal fibrils deriving from the pigment cell-specific pre-melanosomal protein (PMEL). In the lumen of melanosomes, PMEL fibrils optimize sequestration and condensation of the pigment melanin. Interestingly, PMEL fibrils have been described to adopt a typical amyloid-like structure. In contrast to pathological amyloids often associated with neurodegenerative diseases, PMEL fibrils represent an emergent category of physiological amyloids due to their beneficial cellular functions. The formation of PMEL fibrils within melanosomes is tightly regulated by diverse mechanisms, such as PMEL traffic, cleavage and sorting. These mechanisms revealed increasing analogies between the formation of physiological PMEL fibrils and pathological amyloid fibrils. In this review we summarize the known mechanisms of PMEL fibrillation and discuss how the recent understanding of physiological PMEL amyloid formation may help to shed light on processes involved in pathological amyloid formation.
Insights
Physiological amyloid fibrils formed by pre-melanosomal protein (PMEL) in melanosomes are crucial for melanin synthesis. Understanding PMEL fibrillation offers insights into pathological amyloid formation in diseases.
Area of Science:
- Cell Biology
- Biochemistry
- Structural Biology
Background:
- Melanin synthesis occurs in melanosomes, specialized organelles within pigment cells.
- Melanosome biogenesis involves the formation of pre-melanosomal protein (PMEL) fibrils, essential for melanin sequestration.
- PMEL fibrils exhibit amyloid-like structures, functioning as physiological amyloids.
Purpose of the Study:
- To review the mechanisms of PMEL fibrillation within melanosomes.
- To explore the analogies between physiological PMEL amyloid formation and pathological amyloidogenesis.
- To discuss how studying PMEL may illuminate neurodegenerative disease mechanisms.
Main Methods:
- Literature review of PMEL structure, function, and regulation.
- Comparative analysis of PMEL fibrillation and amyloid formation pathways.
- Synthesis of current knowledge on melanosome biogenesis and amyloid structure.
Main Results:
- PMEL fibrils are integral to melanosome function, optimizing melanin condensation.
- PMEL fibrillation is a tightly regulated process involving protein traffic, cleavage, and sorting.
- Significant parallels exist between the formation of physiological PMEL amyloids and pathological amyloids.
Conclusions:
- PMEL fibrillation represents a unique class of functional amyloid.
- Understanding PMEL regulation provides a model for studying amyloid diseases.
- This review bridges the gap between pigment cell biology and neurodegenerative disease research.
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