Isoform‐specific responses of metallothioneins in a marine pollution biomonitor, the green‐lipped mussel Perna viridis, towards different stress stimulations

Abstract

Metallothioneins (MTs) are commonly used as biomarker for metal pollution assessment in marine ecosystems. Using integrated genomic and proteomic analyses, this study characterized two types of MT isoform in the digestive gland of a common biomonitor, the green-lipped mussel Perna viridis, towards the challenges of a metal (cadmium; Cd) and a non-metal oxidant (hydrogen peroxide; H2 O2 ) respectively. The two isoforms differed in their deduced protein sequences, with 73 amino acids for MT10-I and 72 for MT10-II (a novel type), but both consisted of a high percentage (27.4 to 29.2%) of cysteine. Two-dimensional gel and Western blot showed that the MT proteins were present in multiple isoform spots, and they were further validated to be MT10-I and MT10-II using MS analysis coupled with unrestricted modifications searching. Expression of mRNA revealed that MT10-I responded promptly to Cd but had a lagged induction to H2 O2 treatments, while MT10-II was exclusively induced by Cd treatment over the course of exposure. Expression of the MT proteins also showed a delayed response to H2 O2 , compared to Cd treatments. This study uncovered the potential different functional roles of various MTs isoforms in P. viridis and thus advances the resolution of using MTs as biomarkers in future applications.

Diversification and domain evolution of molluskan metallothioneins: a mini review

“…Molecular phylogenetic analysis of Mytilidae MT domains generated trees consistently comprising of three main clades; clades for mytilid MT10s, P. viridis MTs and mytilid MT20s (Additional file 1: Figure S9). In congruent with the previous phylogenetic results using the entire MT polypeptide region, present phylogenetic analyses using separate domains also suggest the early divergence of P. viridis MTs from the other mytilid orthologs (Leung et al 2014). In the Mytilidae lineage, a critical event before speciation is the divergence of MT10 and MT20 forms (Aceto et al 2011) (Fig.…”

“…Nevertheless, based on their Cys motifs frame, these P. viridis MT-IIs (JN596477 to JN596480) have been proposed as MT10 members. Previous phylogenetic analysis has claimed an early divergence of P. viridis MTs from the main mytilid MT10/MT20 groups (Leung et al 2014). When aligned with other mytilid orthologs, P. viridis MT10-I and/or MT10-II represent several residues distinct from other mytilid MT isoforms.…”

“…In the mytilid mussels, two types of MT isoforms, MT10 and MT20 have been described previously (Aceto et al 2011;Leung et al 2014). These two MT types differ in mass and Cys arrangement.…”

“…MT10 and MT20 have been reported to be functionally differentiated. MT10 has been found to be more abundant than MT20, and hence it could be considered as a main player for the regulation of homeostasis under basal conditions (Leung et al 2014;Lemoine et al 2000). Under metal-exposed conditions, MT10 and MT20 have been known to display differential responses and binding ability to essential and non-essential metals.…”

“…The prototypic MT has been supposed to go through further diversification into various distinguished isoforms in different taxa. This evolutionary theory has been comprehensively addressed with several well-known molluskan models such as oysters, mussels and air-breathing snails (Leignel and Laulier 2006;Jenny et al 2016;Palacios et al 2011;Aceto et al 2011;Leung et al 2014). However, in contrast to rich information on these popularly studied species, divergent processes of MTs in other mollusk species (in both gastropods and bivalves) have been quite limitedly explored yet.…”