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.

Growth Hormone(s), Testosterone, Insulin-Like Growth Factors, and Cortisol: Roles and Integration for Cellular Development and Growth With Exercise

“…A major advance in understanding packaging mechanisms of GH molecules within a secretory granule came from the reports of Maji and co-workers showing that the hormone is stored as an amyloid (124,125). Amyloids are defined by their highly organized cross B-sheet regions in protein aggregates and should be considered as yet another level of protein structure.…”

Staphylococcus aureus PSMα3 Cross-α Fibril Polymorphism and Determinants of Cytotoxicity

“…Several PSM members were shown to form amyloid fibrils, essential to their activity (Marinelli et al, 2016;Salinas et al, 2018;Schwartz et al, 2012;Tayeb-Fligelman et al, 2017). Amyloids are structured protein aggregates mostly known for their association with systemic and neurodegenerative diseases (Eisenberg and Jucker, 2012;Knowles et al, 2014;Tycko, 2015), but are also involved in various physiological functions in humans and in microbes (Chapman et al, 2002; DePas and Chapman, 2012;Fowler et al, 2005;Hughes et al, 2018;Jacob et al, 2016;Maji et al, 2009;Otzen and Nielsen, 2008;Pham et al, 2014;Schwartz et al, 2012;Soragni et al, 2015). They are known to form highly stable cross-β fibrils composed of tightly mated β-sheets, with β-strands oriented perpendicularly to the fibril axis (Eisenberg and Sawaya, 2017;Knowles et al, 2007).…”

Artificial Inclusion Bodies for Clinical Development

“…This multiple step procedure (ms), was developed to imitate the dual, sponge-like networks in natural IBs. In a simpler single-step (ss) approach, divalent cations (Zn, in form of ZnCl 2 ), involved in amyloid formation [14] and generically, in protein-protein contacts, [15] were added to a protein solution (Figure 1a). In a simpler single-step (ss) approach, divalent cations (Zn, in form of ZnCl 2 ), involved in amyloid formation [14] and generically, in protein-protein contacts, [15] were added to a protein solution (Figure 1a).…”