Challenging the Metallothionein (MT) Gene of Biomphalaria glabrata: Unexpected Response Patterns Due to Cadmium Exposure and Temperature Stress.

Michael Niederwanger,Reinhard Dallinger,Martin Dvorak,Veronika Pedrini-Martha,Massimo Bidoli,Raimund Schnegg,Katharina Bacher

doi:10.3390/ijms18081747

Michael Niederwanger, Reinhard Dallinger + Show 5 more

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https://doi.org/10.3390/ijms18081747

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Abstract

Metallothioneins (MTs) are low-molecular-mass, cysteine-rich, metal binding proteins. In most animal species, they are involved in metal homeostasis and detoxification, and provide protection from oxidative stress. Gastropod MTs are highly diversified, exhibiting unique features and adaptations like metal specificity and multiplications of their metal binding domains. Here, we show that the MT gene of Biomphalaria glabrata, one of the largest MT genes identified so far, is composed in a unique way. The encoding for an MT protein has a three-domain structure and a C-terminal, Cys-rich extension. Using a bioinformatic approach involving structural and in silico analysis of putative transcription factor binding sites (TFBs), we found that this MT gene consists of five exons and four introns. It exhibits a regulatory promoter region containing three metal-responsive elements (MREs) and several TFBs with putative involvement in environmental stress response, and regulation of gene expression. Quantitative real-time polymerase chain reaction (qRT-PCR) data indicate that the MT gene is not inducible by cadmium (Cd) nor by temperature challenges (heat and cold), despite significant Cd uptake within the midgut gland and the high Cd tolerance of metal-exposed snails.

Highlights

The adaptation process of animal species towards stressful conditions is achieved, among other methods, by relying on an array of “stress”-related gene encoding for proteins enabling protection against adverse environmental conditions, repair of damaged macromolecules, and detoxification of unwanted metal ions
The MT gene of Biomphalaria glabrata is more than 11,000 bp long
The translated coding region represented by the five exons (Figure 1B) spans 369 bp and was confirmed by sequencing of polymerase chain reaction (PCR)-amplified and cloned individual samples

Summary

Introduction

The adaptation process of animal species towards stressful conditions is achieved, among other methods, by relying on an array of “stress”-related gene encoding for proteins enabling protection against adverse environmental conditions, repair of damaged macromolecules, and detoxification of unwanted metal ions. MTs are hydrophilic, low-molecular-mass proteins binding with high affinity to a number of transition metal ions such as Cd2+, Zn2+ and Cu+ [3,4,5] One of their most distinctive properties is the high cysteine content (up to ~30%) with individual cysteine residues arranged in distinctive motifs (e.g., Cys-x-Cys, Cys-x-x-Cys) that form metal-binding clusters. Owing to their features, MTs are often involved in the homeostatic regulation and detoxification of metallic trace elements [6,7]. MTs may participate in the cellular protection from oxidative stress [8,9]

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