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J Mol Biol. 2006 Sep 15;362(2):287-97. Epub 2006 Aug 14.

A novel haem-binding interface in the 22 kDa haem-binding protein p22HBP.

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School of Molecular and Microbial Biosciences, University of Sydney, NSW 2006, Australia.


The 22 kDa haem-binding protein, p22HBP, is highly expressed in erythropoietic tissues and binds to a range of metallo- and non-metalloporphyrin molecules with similar affinities, suggesting a role in haem regulation or synthesis. We have determined the three-dimensional solution structure of p22HBP and mapped the porphyrin-binding site, which comprises a number of loops and a alpha-helix all located on a single face of the molecule. The structure of p22HBP is related to the bacterial multi-drug resistance protein BmrR, and is the first protein with this fold to be identified in eukaryotes. Strikingly, the porphyrin-binding site in p22HBP is located in a similar position to the drug-binding site of BmrR. These similarities suggest that the broad ligand specificity observed for both BmrR and p22HBP may result from a conserved ligand interaction mechanism. Taken together, these data suggest that the both the fold and its associated function, that of binding to a broad range of small hydrophobic molecules, are ancient, and have been adapted throughout evolution for a variety of purposes.

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