Ni2+-Assisted Hydrolysis May Affect the Human Proteome; Filaggrin Degradation Ex Vivo as an Example of Possible Consequences.

Ewa Izabela Podobas,Wojciech Bal,Tomasz Frączyk,Dawid Płonka,Aleksandra Gruca,Jarosław Poznański,Graham Ogg,Sébastien Moretti,Arkadiusz Bonna,Danuta Gutowska-Owsiak,Marcin Grynberg,Mariusz Kulińczak

doi:10.3389/fmolb.2022.828674

Abstract

Deficiency in a principal epidermal barrier protein, filaggrin (FLG), is associated with multiple allergic manifestations, including atopic dermatitis and contact allergy to nickel. Toxicity caused by dermal and respiratory exposures of the general population to nickel-containing objects and particles is a deleterious side effect of modern technologies. Its molecular mechanism may include the peptide bond hydrolysis in X1-S/T-c/p-H-c-X2 motifs by released Ni2+ ions. The goal of the study was to analyse the distribution of such cleavable motifs in the human proteome and examine FLG vulnerability of nickel hydrolysis. We performed a general bioinformatic study followed by biochemical and biological analysis of a single case, the FLG protein. FLG model peptides, the recombinant monomer domain human keratinocytes in vitro and human epidermis ex vivo were used. We also investigated if the products of filaggrin Ni2+-hydrolysis affect the activation profile of Langerhans cells. We found X1-S/T-c/p-H-c-X2 motifs in 40% of human proteins, with the highest abundance in those involved in the epidermal barrier function, including FLG. We confirmed the hydrolytic vulnerability and pH-dependent Ni2+-assisted cleavage of FLG-derived peptides and FLG monomer, using in vitro cell culture and ex-vivo epidermal sheets; the hydrolysis contributed to the pronounced reduction in FLG in all of the models studied. We also postulated that Ni-hydrolysis might dysregulate important immune responses. Ni2+-assisted cleavage of barrier proteins, including FLG, may contribute to clinical disease associated with nickel exposure.

Highlights

Prevalence of nickel alloys in the industry and daily use items is inadvertently associated with the occupational and environmental exposure to airborne particles containing nickel oxides and salts, and to Ni2+ ions present in water and food and released from nickel alloys (World Health Organization, 2000; Kasprzak et al, 2003; Nieminen et al, 2007; Zambelli et al, 2016; Ahlström et al, 2019)
The initial UniProt data were cleaned by suitable word filters to eliminate duplicates, while all protein isomers were included to obtain full representation of the functional proteome
Nickel deposition and stratum corneum penetration seems to be significant after relatively short exposure (Ahlström et al, 2018)

Summary

Introduction

Prevalence of nickel alloys in the industry and daily use items is inadvertently associated with the occupational and environmental exposure to airborne particles containing nickel oxides and salts, and to Ni2+ ions present in water and food and released from nickel alloys (by dermal contact) (World Health Organization, 2000; Kasprzak et al, 2003; Nieminen et al, 2007; Zambelli et al, 2016; Ahlström et al, 2019). The Ni2+-assisted peptide bond hydrolysis (Nihydrolysis) is one such reaction, occurring selectively before S/T in proteins bearing X1-S/T-c/p-H-c-X2 motifs (Ni-hydrolytic motifs, excluding P at the third and reduced C at the first, third and fifth residues within the motif) exposed to Ni2+ ions in solution (Kopera et al, 2010; Krezel et al, 2010; Podobas et al, 2014). The reaction rate depends on pH, temperature and the bulkiness of the first, third and fifth residues, being significantly faster for X1 = G (fast motifs) (Ariani et al, 2013) The effectiveness this process was proven for Cu2+ (Bal et al, 2000) and Pd2+ ions (Wezynfeld et al, 2016), but Ni-hydrolysis was investigated to the largest extent, due to its higher efficiency. Co2+ and Zn2+ ions were proven to be non-reactive in this respect (Bal et al, 2000)

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