“Mercury transporter”的意思、由来-开放百科全书

The mercury transporter superfamily (TC# 1.A.72) is a family of transmembrane bacterial transporters of mercury ions. The common origin of all Mer superfamily members has been established.^[2] The common elements between family members are included in TMSs 1-2. A representative list of the subfamilies and proteins that belong to those subfamilies is available in the Transporter Classification Database.

Subfamilies

Transport Reaction

MerF

The MerF protein encoded on plasmid pMER327/419 is an 81 residue polypeptide with two putative TMSs.^[3] It catalyzes uptake of Hg²⁺ in preparation for reduction by mercuric reductase. The MerF gene is found on mercury resistant plasmids from many gram-negative bacteria, but the sequence of the protein from these plasmids is the same. Limited sequence similarity is shown with the first two TMSs of MerT (TC# 1.A.72.3) and MerC (TC# 1.A.72.4). MerF has two vicinal pairs of cysteine residues which are involved in the transport of Hg(II) across the membrane and are exposed to the cytoplasm.^[4] Some members of the MerF family have been designated MerH.^[5]

Crystal structures

MerTP

The MerTP permeases catalyze uptake into bacterial cells of Hg²⁺ in preparation for its reduction by the MerA mercuric reductase. The Hg^o produced by MerA is volatile and passively diffuses out of the cell. The merT and merP genes are found on mercury resistance plasmids and transposons of gram-negative and gram-positive bacteria but are also chromosomally encoded in some bacteria. MerT consists of about 130 amino acids and has 3 transmembrane helical segments.^[6] Operon analyses have been reported.^[3]^[7]^[8]

MerP

MerP is a periplasmic Hg²⁺-binding receptor of about 70-80 amino acyl residues, synthesized with a cleavable N-terminal leader. It is homologous to the N-terminal heavy metal binding domains of the copper-and cadmium-transporting P-type ATPases. The 3-D structure of MerP from Ralstonia metallidurans has been solved to 2 Å resolution ({{PDB|1OSD}}).^[9]^[10] It is 91 amino acyl residues (aas) long with its leader sequence, is monomeric, and binds a single Hg²⁺ ion. Hg²⁺ is bound to a sequence GMTCXXC found in metallochaperones as well as metal-transporting ATPases. The fold is βαββαβ, called the ''ferridoxin-like fold''.

MerT

MerT homologues have been identified in which the 3 TMS MerT is fused to a MerP ''heavy metal associated'' (HMA) domain, possibly via a linker region that includes a fourth TMS (see 1.A.72.3.3). HMA domains of ~30 aas are found in MerP, copper chaperone proteins, mercuric reductase, and at the N-termini of both copper and heavy metal P-type ATPases, sometimes in multiple copies.^[11]

MerC

The MerC protein encoded on the IncJ plasmid pMERPH of the Shewanella putrefaciens mercuric resistance operon is 137 amino acids in length and possesses four putative transmembrane α-helical spanners (TMSs). It has been shown to bind and take up Hg²⁺ ions. merC genes are encoded on several plasmids of gram-negative bacteria and may also be chromosomally encoded. MerC proteins are homologous to other bacterial Hg²⁺ bacterial transporters.^[2]^[12]^[13]^[14]

MerE

See {{Cite journal|title = The MerE protein encoded by transposon Tn21 is a broad mercury transporter in Escherichia coli|journal = FEBS Letters|date = 2009-04-02|issn = 1873-3468|pmid = 19265693|pages = 1127–1131|volume = 583|issue = 7|doi = 10.1016/j.febslet.2009.02.039|first = Masako|last = Kiyono|first2 = Yuka|last2 = Sone|first3 = Ryosuke|last3 = Nakamura|first4 = Hidemitsu|last4 = Pan-Hou|first5 = Kou|last5 = Sakabe}}

References

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