1jqf
From Proteopedia
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'''Human Transferrin N-Lobe Mutant H249Q''' | '''Human Transferrin N-Lobe Mutant H249Q''' | ||
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[[Category: MacGillivray, R T.A.]] | [[Category: MacGillivray, R T.A.]] | ||
[[Category: Mason, A B.]] | [[Category: Mason, A B.]] | ||
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Revision as of 18:38, 2 May 2008
Human Transferrin N-Lobe Mutant H249Q
Overview
Proteins of the transferrin (Tf) family play a central role in iron homeostasis in vertebrates. In vertebrate Tfs, the four iron-binding ligands, 1 Asp, 2 Tyr, and 1 His, are invariant in both lobes of these bilobal proteins. In contrast, there are striking variations in the Tfs that have been characterized from insect species; in three of them, sequence changes in the C-lobe binding site render it nonfunctional, and in all of them the His ligand in the N-lobe site is changed to Gln. Surprisingly, mutagenesis of the histidine ligand, His249, to glutamine in the N-lobe half-molecule of human Tf (hTf/2N) shows that iron binding is destabilized and suggests that Gln249 does not bind to iron. We have determined the crystal structure of the H249Q mutant of hTf/2N and refined it at 1.85 A resolution (R = 0.221, R(free) = 0.246). The structure reveals that Gln249 does coordinate to iron, albeit with a lengthened Fe-Oepsilon1 bond of 2.34 A. In every other respect, the protein structure is unchanged from wild-type. Examination of insect Tf sequences shows that the K206.K296 dilysine pair, which aids iron release from the N-lobes of vertebrate Tfs, is not present in the insect proteins. We conclude that substitution of Gln for His does destabilize iron binding, but in the insect Tfs this is compensated by the loss of the dilysine interaction. The combination of a His ligand with the dilysine pair in vertebrate Tfs may have been a later evolutionary development that gives more sophisticated pH-mediated control of iron release from the N-lobe of transferrins.
About this Structure
1JQF is a Single protein structure of sequence from Homo sapiens. Full crystallographic information is available from OCA.
Reference
Ligand variation in the transferrin family: the crystal structure of the H249Q mutant of the human transferrin N-lobe as a model for iron binding in insect transferrins., Baker HM, Mason AB, He QY, MacGillivray RT, Baker EN, Biochemistry. 2001 Oct 2;40(39):11670-5. PMID:11570867 Page seeded by OCA on Fri May 2 21:38:38 2008
