TCDB is operated by the Saier Lab Bioinformatics Group
TCIDNameDomainKingdom/PhylumProtein(s)
1.A.72.1:  The MerF Mercuric Ion (Hg²⁺) Uptake (MerF) Family
*1.A.72.1.1









The MerF mercuric ion uptake transporter of 81 aas and 2 TMSs. The NMR structure of the helix-loop-helix core domain of MerF has been determined with a backbone RMSD of 0.58 Å (Howell et al. 2005). Moreover, the fold of this polypeptide demonstrates that the two vicinal pairs of cysteine residues, shown to be involved in the transport of Hg++ across the membrane, are exposed to the cytoplasm. This finding differs from earlier structural and mechanistic models that were based primarily on the somewhat atypical hydropathy plot for MerF and related transport proteins (Howell et al. 2005). 
Bacteria
Proteobacteria
MerF of plasmid pMER327/419 of Pseudomonas aeruginosa
*1.A.72.1.2









Heavy metal transporter

Bacteria
Proteobacteria
HM transporter of Arcobacter butzleri (A8EUY8)
*1.A.72.1.3









MerT (97aas)/MerP (93aas) (in a single operon with a transglutaminase (COG1305)).

Bacteria
Proteobacteria
MerTP of Haemophilus influenzae
MerT (Q57347)
MerP (P71365)
1.A.72.2:  The MerH Mercuric Ion (Hg²⁺) Permease (MerH) Family
*1.A.72.2.1









Hg2+ transporter, MerH (171aas; 4 TMSs) (transports mercuric ions via a pair of essential cysteine residues, but only when coexpressed with the mercuric reductase) (Schué et al., 2009).

Bacteria
Actinobacteria
MerH of Mycobacterium marinum (B2I419)
*1.A.72.2.2









MerC homologue (129aas; 4 TMSs)

Bacteria
Gemmatimonadetes
MerC homologue of Gemmatimonas aurantiaca
1.A.72.3:  The MerTP Mercuric Ion (Hg²⁺) Permease (MerTP) Family
*1.A.72.3.1









MerT/P

Bacteria
Proteobacteria
MerT/P of Ralstonia eutropha (Q6UP69)
*1.A.72.3.2









Putative MerT-MerP fusion protein of 200 aas (3 TMSs)

Bacteria
Bacteroidetes/Chlorobi group
 MerT-MerP of Chryseobacterium gleum (C0YI47)
*1.A.72.3.3









Putative MerT-MerP fusion protein of 199 aas (3-4 TMSs)

Bacteria
Chlamydiae/Verrucomicrobia group
MerT-MerP of Methylacidiphilum infernorum (B3DYY6)
*1.A.72.3.4









Putative MerT-MerP fusion protein of 196 aas (3 TMSs)

Bacteria
Bacteroidetes/Chlorobi group
MerT-MerP of Spirosoma linguale (D2QV66)
*1.A.72.3.5









Mercuric ion uptake system, MerT-P/MerP

Bacteria
Bacteroidetes/Chlorobi group
MerT-P/MerP of Tenacibaculum discolor
MerT-P (204aas; H6WCN3)
MerP (113aas; H6WCN4) 
1.a.72.4:  The MerC Mercuric Ion (Hg²⁺) Permease (MerC) Family
*1.A.72.4.1









MerC

Bacteria
Proteobacteria
MerC of the IncJ plasmid pMERPH of Shewanella putrefaciens
*1.A.72.4.2









Mercuric transport channel protein, MerC, of 144 aas and 4 TMSs.  Cys-23 and Cys-26 of the protein were involved in Hg2+-recognition/uptake, but Cys-132 and Cys-137 were not (Sasaki et al. 2005). E. coli cells producing MerC were hypersensitive to CdCl2. In this case, mutation of His72 rendered the host cells less CdCl2 sensitive, whereas none of the Cys residues affected it. E. coli cells expressing a merC-deletion mutant, in which the coding-sequence of the carboxy-terminal cytoplasmic region was removed, retained Hg2+ hypersensitivity and showed about 55% HgCl2 uptake ability compared to that of the one expressing the intact merC, indicating that this region is not essential for Hg2+ uptake. Coexpression of the A. ferrooxidans gene encoding mercuric reductase (merA) and the merC deletion mutation conferred HgCl2 tolerance to E. coli host cells. Under this condition, the merC deletion gene product was exclusively present as a monomer (Sasaki et al. 2005).

Bacteria
Proteobacteria
MerC of Acidithiobacillus ferrooxidans (Thiobacillus ferrooxidans)
1.a.72.5:  The MerE Mercuric Ion (Hg²⁺) Permease (MerE) Family
*1.A.72.5.1









The Mercuric ion (Hg2+) uptake transporter, MerE (78aas; 2 TMSs).

Bacteria
Proteobacteria
MerE of transposon Tn21 of E. coli (Q57069)
*1.A.72.5.2









MerE mercury resistance protein of 89 aas and 2 TMSs.  It has been purified and characterized, and has proven useful for bioremediation (Amin et al. 2019).

Bacteria
Firmicutes
MerE of Bacillus cereus