Co-aggregation and secondary nucleation in the life cycle of human prolactin/galanin functional amyloids.

Debdeep Chatterjee,Praful Singru,Laxmikant Gadhe,Sakunthala Arunima,Chinmai Pindi,Debalina Datta,Reeba S Jacob,Namrata Singh,Ambuja Navalkar,Pradeep Kadu,Shinjinee Sengupta,Samir K Maji,Ajoy Paul,Santosh Kumar,Sanjib Senapati,Surabhi Mehra,Soumik Ray

doi:10.7554/elife.73835

Abstract

Synergistic-aggregation and cross-seeding by two different proteins/peptides in the amyloid aggregation are well evident in various neurological disorders including Alzheimer's disease. Here, we show co-storage of human Prolactin (PRL), which is associated with lactation in mammals, and neuropeptide galanin (GAL) as functional amyloids in secretory granules (SGs) of the female rat. Using a wide variety of biophysical studies, we show that irrespective of the difference in sequence and structure, both hormones facilitate their synergic aggregation to amyloid fibrils. Although each hormone possesses homotypic seeding ability, a unidirectional cross-seeding of GAL aggregation by PRL seeds and the inability of cross seeding by mixed fibrils suggest tight regulation of functional amyloid formation by these hormones for their efficient storage in SGs. Further, the faster release of functional hormones from mixed fibrils compared to the corresponding individual amyloid, suggests a novel mechanism of heterologous amyloid formation in functional amyloids of SGs in the pituitary.

Highlights

Protein/peptide misfolding, aggregation, and amyloid formation is associated with various neurological disorders such as Alzheimer’s disease and Parkinson’s disease1,2
Double immunofluorescence of PRL and GAL along with amyloid specific OC antibody showed strong colocalization suggesting both the hormones are in the amyloid state (Figure 1e), which was observed in Thioflavin S (ThioS) staining (Figure 1-figure supplement 1)
In contrast to the female rats, when a similar study of double immunofluorescence was performed in the male rat pituitary tissues, we did not observe any co-localization of PRL and GAL

Summary

Introduction

Protein/peptide misfolding, aggregation, and amyloid formation is associated with various neurological disorders such as Alzheimer’s disease and Parkinson’s disease. Pmel-17 amyloid fibrils template melanin polymerization inside melanosomes; Curli fibrils of E.coli support the organism to adhere to a surface and help their colonization process inside biofilms13,14 In this line, another very interesting aspect is the formation of functional amyloid by protein/peptide hormones (such as prolactin (PRL) and galanin (GAL)) during their storage inside the secretory granules (SGs) of pituitary. Homotypic aggregation and seeding is the most favored mechanism of protein aggregation and amyloid formation, synergistic aggregation (co-aggregation) by two different proteins/peptides and heterologous seeding are suggested to be involved in many neurodegenerative disorders. Our in vitro release assay showed faster release of functional monomers by heterotypic, hybrid amyloid (PRL-GAL) compared to its homotypic counterparts This supports the storage and release are highly controlled and conserved in pituitary tissue for the optimum function to be served

Results

Discussion

Panda, National Institute of Immunology, New Delhi

Data availability statement