Ligand binding in the conserved interhelical loop of CorA, a magnesium transporter from Mycobacterium tuberculosis.
CorA is a constitutively expressed magnesium transporter in many bacteria. The crystal structures of Thermotoga maritima CorA provide an excellent structural framework for continuing studies. Here, the ligand binding properties of the conserved interhelical loop, the only portion of the protein exposed to the periplasmic space, are characterized by solution nuclear magnetic resonance spectroscopy. Through titration experiments performed on the isolated transmembrane domain of Mycobacterium tuberculosis CorA, it was found that two CorA substrates (Mg2+ and Co2+) and the CorA-specific inhibitor (Co(III) hexamine chloride) bind in the loop at the same binding site. This site includes the glutamic acid residue from the conserved "MPEL" motif. The relatively large dissociation constants indicate that such interactions are weak but not atypical for channels. The present data support the hypothesis that the negatively charged loop could act as an electrostatic ring, increasing local substrate concentrations before transport across the membrane.
Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, USA.
Jian
J
Hu
Mukesh
M
Sharma
Huajun
H
Qin
Fei Philip
FP
Gao
Timothy A
TA
Cross
D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D027682:Cation Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002942:Circular Dichroism; D003001:Cloning, Molecular; D003035:Cobalt / Q000378:metabolism; D017124:Conserved Sequence; D003432:Cross-Linking Reagents / Q000494:pharmacology; D007700:Kinetics; D008024:Ligands; D008274:Magnesium / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009169:Mycobacterium tuberculosis / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017510:Protein Folding; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D020124:Thermotoga maritima / Q000378:metabolism*
D001426:Bacterial Proteins; D027682:Cation Transport Proteins; D003432:Cross-Linking Reagents; D008024:Ligands; D011993:Recombinant Fusion Proteins; D003035:Cobalt; D008274:Magnesium