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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). The apo state positions one of the cysteine pairs closer to the periplasmic side of the membrane, while in the bound state, the same pair approaches the cytoplasmic side (Hwang et al. 2019). This is consistent with the functional requirement of accepting Hg2+ from the periplasmic space, sequestering it on acceptance, and transferring it to the cytoplasm. Conformational changes in the TMSs facilitate the functional interaction of the two cysteine pairs. Free-energy calculations provide a barrier of 16 kcal/mol for the association of the periplasmic Hg2+-bound protein, MerP, with MerF, and 7 kcal/mol for the subsequent association of MerF's two cysteine pairs (Hwang et al. 2019).

Accession Number:Q56446
Protein Name:MerF aka MERT
Length:81
Molecular Weight:8726.00
Species:Pseudomonas fluorescens, OS Xanthomonas sp., OS Comamonas testosteroni (Pseudomonas testosteroni), OS Citrobacter freundii, and OS Escherichia coli [582]
Number of TMSs:2
Location1 / Topology2 / Orientation3: Mitochondrion inner membrane1 / Multi-pass membrane protein2
Substrate Hg2+

Cross database links:

Pfam: PF11431   

References (7)

[1] “Mercury resistance determinants related to Tn21, Tn1696, and Tn5053 in enterobacteria from the preantibiotic era.”  Essa A.M.et.al.   12604550
[2] “Four genes, two ends, and a res region are involved in transposition of Tn5053: a paradigm for a novel family of transposons carrying either a mer operon or an integron.”  Kholodii G.Y.et.al.   8594337
[3] “NMR structure determination of a membrane protein with two transmembrane helices in micelles: MerF of the bacterial mercury detoxification system.”  Howell S.C.et.al.   15794657
[4] “Mercury resistance determinants related to Tn21, Tn1696, and Tn5053 in enterobacteria from the preantibiotic era.”  Essa A.M.et.al.   12604550
[5] “Four genes, two ends, and a res region are involved in transposition of Tn5053: a paradigm for a novel family of transposons carrying either a mer operon or an integron.”  Kholodii G.Y.et.al.   8594337
[6] “NMR structure determination of a membrane protein with two transmembrane helices in micelles: MerF of the bacterial mercury detoxification system.”  Howell S.C.et.al.   15794657
[7] “Structure determination of a membrane protein with two trans-membrane helices in aligned phospholipid bicelles by solid-state NMR spectroscopy.”  De Angelis A.A.et.al.   16967977
Structure:
1WAZ   2H3O   2LJ2   2M67   2MOZ     

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FASTA formatted sequence
1:	MKDPKTLLRV SIIGTTLVAL CCFTPVLVIL LGVVGLSALT GYLDYVLLPA LAIFIGLTIY 
61:	AIQRKRQADA CCTPKFNGVK K