User:Khaja Muneeruddin/Sandbox 1

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One of the CBI Molecules being studied in the University of Massachusetts Amherst Chemistry-Biology Interface Program at UMass Amherst and on display at the Molecular Playground.


is a 80 KDa bilobal, iron binding glycoprotein. In Apo transferrin (iron free form), N-lobe (brown) and C-lobe (green) bind to one ferric ion each to keep ferric ion in solution or transport to iron requiring cells.

N-lobe and C-lobe are homologous and contain identical iron binding amino acid residues. At the binding site of N-lobe Asp63, Tyr188, Tyr95, His249 and Arg-124 are involved in trapping iron[1]. The amino acids involved in trapping of iron at the bind site of C-lobe include Asp392, Tyr426, Tyr517, His585, Arg456. Apart from these amino acid, at both the lobes a carbonate ion also play an important role in binding ferric ion[2]. N lobe and C lobe undergoes a large conformational change upon binding to ferric ion. Open N-lobe characteristics and upon binding to iron closed N lobe looks like this.

Transferrin delivers iron to iron requiring cells by receptor-mediated endocytosis. At basic pH of cell surface diferric HTf binds to human transferrin receptor (hTfR). Upon binding, iron bound hTf-hTfR is internalized in the cell by endocytosis. In the acidic condition of endosome iron is release from hTf into the cells. The ApohTf-HTfR complex is recycled back to the cell surface and at the basic pH of cell surface transferrin unbounds from the TfR[3]. Both N-lobe and C-lobe undergoes

show each binding site and label residues.


References

  1. ↑ MacGillivray RT, Moore SA, Chen J, Anderson BF, Baker H, Luo Y, Bewley M, Smith CA, Murphy ME, Wang Y, Mason AB, Woodworth RC, Brayer GD, Baker EN. Two high-resolution crystal structures of the recombinant N-lobe of human transferrin reveal a structural change implicated in iron release. Biochemistry. 1998 Jun 2;37(22):7919-28. PMID:9609685 doi:10.1021/bi980355j
  2. ↑ Mason AB, Halbrooks PJ, James NG, Connolly SA, Larouche JR, Smith VC, MacGillivray RT, Chasteen ND. Mutational analysis of C-lobe ligands of human serum transferrin: insights into the mechanism of iron release. Biochemistry. 2005 Jun 7;44(22):8013-21. PMID:15924420 doi:10.1021/bi050015f
  3. ↑ Giannetti AM, Halbrooks PJ, Mason AB, Vogt TM, Enns CA, Bjorkman PJ. The molecular mechanism for receptor-stimulated iron release from the plasma iron transport protein transferrin. Structure. 2005 Nov;13(11):1613-23. PMID:16271884 doi:10.1016/j.str.2005.07.016

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Khaja Muneeruddin

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