Cadmium Uptake, MT Gene Activation and Structure of Large-Sized Multi-Domain Metallothioneins in the Terrestrial Door Snail Alinda biplicata (Gastropoda, Clausiliidae)

Abstract

Terrestrial snails (Gastropoda) possess Cd-selective metallothioneins (CdMTs) that inactivate Cd2+ with high affinity. Most of these MTs are small Cysteine-rich proteins that bind 6 Cd2+ equivalents within two distinct metal-binding domains, with a binding stoichiometry of 3 Cd2+ ions per domain. Recently, unusually large, so-called multi-domain MTs (md-MTs) were discovered in the terrestrial door snail Alinda biplicata (A.b.). The aim of this study is to evaluate the ability of A.b. to cope with Cd stress and the potential involvement of md-MTs in its detoxification. Snails were exposed to increasing Cd concentrations, and Cd-tissue concentrations were quantified. The gene structure of two md-MTs (9md-MT and 10md-MT) was characterized, and the impact of Cd exposure on MT gene transcription was quantified via qRT PCR. A.b. efficiently accumulates Cd at moderately elevated concentrations in the feed, but avoids food uptake at excessively high Cd levels. The structure and expression of the long md-MT genes of A.b. were characterized. Although both genes are intronless, they are still transcribed, being significantly upregulated upon Cd exposure. Overall, our results contribute new knowledge regarding the metal handling of Alinda biplicata in particular, and the potential role of md-MTs in Cd detoxification of terrestrial snails, in general.

Modularity in Protein Evolution: Modular Organization and De Novo Domain Evolution in Mollusk Metallothioneins

“…2017 ; Schmielau et al. 2019 ; Pedrini-Martha et al. 2020 ), and our results have increased this list with 16 new proteins containing a variable number of repeated domains.…”

“…Species of Lymnaeidae, for instance, lacked the last [CxC] motif of the β1 domain, MTs of Bradybaena similaris and Fiona pinnata had an additional β3 domain (i.e., β3.1/β3.2) ( supplementary fig. S2 D , Supplementary Material online), and Alinda biplicata AbiMT3 and AbiMT4 had eight and nine β3 domains, respectively ( Pedrini-Martha et al. 2020 ).…”

“…2012 ) or expansions of MT domains ( Tanguy and Moraga 2001 ; Jenny et al. 2016 ; Pedrini-Martha et al. 2020 ), along with elevated levels of MT expression ( Timmermans et al.…”

Responsiveness of metallothionein and hemocyanin genes to cadmium and copper exposure in the garden snail Cornu aspersum

“…Whereas CdMT gene expression was manifold upregulated in the midgut gland and mantle of Cd‐exposed individuals, CuMT transcription was significantly upregulated only in the midgut gland of Cu‐stressed snails. Cd‐dependent CdMT gene upregulation was so far observed in all studies using terrestrial snail species of the clade of Stylommatophora (Palacios et al, 2011; Pedrini‐Martha et al, 2020), including C. aspersum (Höckner et al, 2011). In contrast, only transient or no upregulation at all of snail CuMT genes can be detected after Cu exposure (Höckner et al, 2011; Palacios et al, 2011).…”

The Enigmatic Metallothioneins: A Case of Upward-Looking Research

“…Genetic and biochemical data from mollusks suggests that MTs might have played crucial roles in metal detoxification throughout early evolution. More recently, MTs may have become relevant for homeostasis as living beings adapted to increasingly variable environments [ 40 , 92 , 93 , 94 , 95 ]. Since MTs are somewhat flexible and can change in response to environmental factors, their various forms might have been crucial for organisms to adapt to variable situations of metal bioavailability.…”