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PDB:2BBJ

Protein Name

CorA Mg2+ transporter

Species

Thermotoga maritima (bacteria, thermophile)

Biological Context

The magnesium ion, Mg2+, is essential for many biochemical reactions, signaling, enzyme activation, plant photosynthesis, and so on. Neither the shortage nor excess is not good for life. Therefore precise control of Mg2+ uptake and excretion is indispensable. However, the mechanism of Mg2+ transport remains unknown. Though many of the proteins involved in transporting Mg2+ are not identified, CorA is probably one such protein which uptakes Mg2+ in bacteria.

Structure Description

2bbj2bbj_x2bbj_y

The structure shown here is the CorA magnesium transporter which is a homopentamer with five-fold symmetry about a central pore and can be divided into three parts(Fig.1).

monomer (Fig.1) The structure of monomer.
Blue:transmembrane domain (the pale is TM1, the dark is TM2,respectively)
Light blue:the helix forming inner wall of funnel (helix 7)
Purple:cytoplasmic domain

A carboxy-terminal transmembrane domain comprises two transmembrane helices, TM1 and TM2, from each monomer. The middle portion resembles a funnel, narrow at the entrance (under 5 angstrom) and wide at the mouth (under 20 angstrom), that is formed largely by a long a-helix extension of the inner transmembrane helix. Finally, a cytoplasmic domain lies exterior to the funnel.

A carboxy-terminal transmembrane domain comprises two transmembrane helices, TM1 and TM2, from each monomer. The middle portion resembles a funnel, narrow at the entrance (under 5 angstrom) and wide at the mouth (under 20 angstrom), that is formed largely by a long a-helix extension of the inner transmembrane helix. Finally, a cytoplasmic domain lies exterior to the funnel.

 The cytoplasmic domain of CorA is a seven-stranded parallel/antiparallel beta-sheet sandwiched between two sets of a-helices (alpha1, 2, and 3) and (alpha4, 5, and 6). In the long alpha 7 helix in the middle of sequence (residues 251-312) consists of inner funnel at the part of N-terminal, and transmembrane domain TM1 at the part of C-terminal. This alpha helix which is called stalk helix kinks as it enters the membrane,extends through the membrane, forms the first transmembrane helix (TM1). Five TM1s form the inner wall of the pore, and the following TM2s surround TM1s then construct double ring (Fig.2).

(Fig.2) Transmembrane domain shown from outer side (periplasm side) of plasma membrane.
Inner pale blue is TM1 domain, and dark blue is TM2 domain, respectively.

The pore which is formed by the transmembrane domain has three narrow part and two wide part alternately. This structure is found in other ion channels and can help to stabilize an ion. At the cytoplasm side surface of transmembrane domain, there are lysines, with positive charge, from TM2 helix of the C-terminal part of transmembrane domain and stalk helix. At the following cytoplasm domain has negatively charged residues, aspartate or glutamate. The sequense of this area is well conserved.

Protein Data Bank (PDB)

References

Source

  • Lunin, V.V. Dobrovetsky, E. Khutoreskaya, G. Zhang, R. Joachimiak, A. Doyle, D.A. Bochkarev, A. Maguire, M.E. Edwards, A.M. Koth, C.M.; "Crystal structure of the CorA Mg2+ transporter"; Nature; (2006) 440:833-837 PubMed:16598263.

Others

author: Kudou Takahiro


Japanese version:PDB:2BBJ