Structural Adaptation of a Protein to Increased Metal Stress: NMR Structure of a Marine Snail Metallothionein with an Additional Domain

Abstract

In this study, we present an NMR structure of the metallothionein (MT) from the snail Littorina littorea (LlMT) in complex with Cd . LlMT is capable of binding 9 Zn or 9 Cd ions. Sequence alignments with other snail MTs revealed that the protein is likely composed of three domains. The study revealed that the protein is divided into three individual domains, each of which folds into a single well-defined three-metal cluster. The central α2 and C-terminal β domains are positioned with a unique relative orientation. Two variants with longer and shorter linkers were investigated, which revealed that specific interdomain contacts only occurred with the wild-type linker. Moreover, a domain-swap mutant in which the highly similar α1 and α2 domains were exchanged was structurally almost identical. It is suggested that the expression of a three-domain MT confers an evolutionary advantage on Littorina littorea in terms of coping with Cd stress and adverse environmental conditions.

A histidine-richPseudomonasmetallothionein with a disordered tail displays higher binding capacity for cadmium than zinc

“…66,67 Similar 113 Cd chemical shifts that arise from increased shielding were also reported in Littorina litorea MT (516 ppm) and the α-domain of human MT-3 (595 ppm) where they were attributed to transient binding or discrepancy in coordination environment, respectively. 39,68 The observed reduced thermodynamic stability of the fourth Cd II ion in the Cd 4 sh_PflQ2 MT, and hence Cd(C), corroborates this interpretation. The proposed equilibrium and thus the interchange of thiolate ligand C10 must be reflected by remarkable intra-cluster dynamics.…”

“…All metal pseudo-residues were created using the Maestro program (Schrödinger, USA) in a similar manner as described before. 39 (Table S3). More details on the structure calculation protocol will be reported elsewhere.…”

“…6 However, in the last decade, multiple examples of MTs emerged that challenge this assumption by showing a preference either for Cd II or Zn II . 31,39,46,47 In addition, a positive correlation has been proposed between the formation of homogeneous well-folded structures upon binding of a specific metal ion and the biological relevance of that metal. [46][47][48][49][50][51][52][53][54][55][56][57] Due to the promiscuous nature of MTs, their metal preference is probably also strongly affected by the local abundance of the respective metal ion in the native organism or its environment.…”

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

“…More recent studies demonstrate, however, a greater variability of gastropod MT protein structures than so far known. The marine periwinkle Littorina littorea and its terrestrial relative Pomatias elegans, for example, have increased the metal-binding capacity of their Cd-selective MTs by addition of a third Cd-binding domain, derived from a duplication of their N-terminal domain [26,27]. Consequently, these newly discovered three-domain MTs have increased their binding stoichiometry from 6 to 9 Cd 2+ ions [26,28].…”

“…The marine periwinkle Littorina littorea and its terrestrial relative Pomatias elegans, for example, have increased the metal-binding capacity of their Cd-selective MTs by addition of a third Cd-binding domain, derived from a duplication of their N-terminal domain [26,27]. Consequently, these newly discovered three-domain MTs have increased their binding stoichiometry from 6 to 9 Cd 2+ ions [26,28]. Our most recent studies indicate the presence of multi-domain MTs (md-MTs) with as much as eight (8) metal-binding domains (8md-MT) in an MT of the freshwater snail Marisa cornuarietis, and with nine (9) or even ten (10) metal-binding domains (9md-MT and 10md-MT) in two MT isoforms of the terrestrial snail A. biplicata [19].…”