title: Amyloid formation of growth hormone in presence of zinc: Relevance to its storage in secretory granules.
abstract: Amyloids are cross-β-sheet fibrillar aggregates, associated with various human diseases and native functions such as protein/peptide hormone storage inside secretory granules of neuroendocrine cells. In the current study, using amyloid detecting agents, we show that growth hormone (GH) could be stored as amyloid in the pituitary of rat. Moreover, to demonstrate the formation of GH amyloid in vitro, we studied various conditions (solvents, glycosaminoglycans, salts and metal ions) and found that in presence of zinc metal ions (Zn(II)), GH formed short curvy fibrils. The amyloidogenic nature of these fibrils was examined by Thioflavin T binding, Congo Red binding, transmission electron microscopy and X-ray diffraction. Our biophysical studies also suggest that Zn(II) initiates the early oligomerization of GH that eventually facilitates the fibrillation process. Furthermore, using immunofluorescence study of pituitary tissue, we show that GH in pituitary significantly co-localizes with Zn(II), suggesting the probable role of zinc in GH aggregation within secretory granules. We also found that GH amyloid formed in vitro is capable of releasing monomers. The study will help to understand the possible mechanism of GH storage, its regulation and monomer release from the somatotrophs of anterior pituitary.
authors.affiliation: Department of Biosciences and Bioengineering, IIT Bombay Mumbai, India 400 076.
authors.forename: Reeba S
authors.initials: RS
authors.lastname: Jacob
authors.affiliation: Department of Biosciences and Bioengineering, IIT Bombay Mumbai, India 400 076.|IITB Monash Research Academy, IIT Bombay, Powai, Mumbai 400076, India.
authors.forename: Subhadeep
authors.initials: S
authors.lastname: Das
authors.affiliation: Department of Biosciences and Bioengineering, IIT Bombay Mumbai, India 400 076.
authors.forename: Saikat
authors.initials: S
authors.lastname: Ghosh
authors.affiliation: Department of Biosciences and Bioengineering, IIT Bombay Mumbai, India 400 076.
authors.forename: Arunagiri
authors.initials: A
authors.lastname: Anoop
authors.affiliation: Department of Biosciences and Bioengineering, IIT Bombay Mumbai, India 400 076.
authors.forename: Narendra Nath
authors.initials: NN
authors.lastname: Jha
authors.affiliation: Department of Chemistry, IIT Bombay Mumbai, India 400076.
authors.forename: Tuhin
authors.initials: T
authors.lastname: Khan
authors.affiliation: School of Biological Sciences, National Institute of Science Education and Research, Bhubaneswar, India.
authors.forename: Praful
authors.initials: P
authors.lastname: Singru
authors.affiliation: Department of Biosciences and Bioengineering, IIT Bombay Mumbai, India 400 076.
authors.forename: Ashutosh
authors.initials: A
authors.lastname: Kumar
authors.affiliation: Department of Biosciences and Bioengineering, IIT Bombay Mumbai, India 400 076.
authors.forename: Samir K
authors.initials: SK
authors.lastname: Maji
mesh_terms: D000682:Amyloid / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D019382:Human Growth Hormone / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008854:Microscopy, Electron; D008958:Models, Molecular; D010902:Pituitary Gland / Q000378:metabolism*; D017433:Protein Structure, Secondary; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D022142:Secretory Vesicles / Q000378:metabolism; D012997:Solvents / Q000494:pharmacology; D014961:X-Ray Diffraction / Q000379:methods; D015032:Zinc / Q000494:pharmacology*
chemical_list: D000682:Amyloid; D011994:Recombinant Proteins; D012997:Solvents; D019382:Human Growth Hormone; D015032:Zinc