Proteins involved in iron metabolism
Dr. Mason received her Ph.D. in Biochemistry at Boston University in 1979 for structural work on a blue algal protein, phycocyanin, determining the primary structure of the two subunits of phycocyanin and how the blue linear tetrapyrrole was attached to the protein. In 1979, Dr. Mason came to the University of Vermont to work on the iron binding protein, transferrin. She is currently a Research Professor of Biochemistry.
Members of the transferrin family (serum transferrin, ovotransferrin & lactoferrin) bind iron with different affinities in each of two lobes, although all lobes have identical amino acid ligands to the iron. Iron sequestration and transport by serum transferrin and delivery of this iron to cells by pH dependant, receptor mediated endocytosis, are biologically critical functions. Our research seeks to mechanistically understand iron release from the individual lobes of human serum transferrin and ovotransferrin, especially in a complex with their respective receptors. We believe that both lobes of transferrin interact with each other and with the receptor to bring about release of this vital metal. Key to our work is our ability to make site-directed mutants for which spectral properties (UV-vis and EPR) and the rate constants for iron release in the presence and absence of our recombinant soluble transferrin receptor (as a function of pH and anion concentration) can be measured. Authentic monoferric and apo-transferrins provide essential controls. The conformational dependence on recognition of the mutants by the receptor can be assessed by surface plasmon resonance (SPR) measurements to obtain affinity constants as a function of pH and iron saturation. Some samples are further evaluated by isothermal titration calorimetry (ITC) to provide thermodynamic parameters to more precisely evaluate the interactions. Equilibrium binding studies and cellular uptake experiments allow further assessment of the interaction between transferrin and the receptor and show whether a particular mutant retains the ability to donate iron to cells. This cell work provides essential in vivo data to support our in vitro studies. Integral to our studies are structure determinations of human serum transferrin and some of our mutants allowing us to link structure to function. Overall we wish to precisely identify the steps leading to iron release by identification of the specific residues within each lobe of transferrin that facilitate the efficient delivery of iron at the right time in the right place. The interaction of TF with its specific receptor controls iron distribution in the body. Owing to the fact that iron deficiency and excess are directly related to specific human diseases, understanding this process at the molecular level is essential to a global understanding of iron metabolism.
Mason, A.B., Byrne, S.L., Everse, S.J., Roberts, S.E., Chasteen, N.D., Smith, V.C., MacGillivray, R.T., Kandemir, B., and Bou-Abdallah, F., A loop in the N-lobe of human serum transferrin is critical for binding to the transferrin receptor as revealed by mutagenesis, isothermal titration calorimetry, and epitope mapping. J Mol Recognit. 2009 Nov-Dec;22(6):521-9
Byrne, S.L., Chasteen, N.D., Steere, A.N., and Mason, A.B., The unique kinetics of iron release from transferrin: the role of receptor, lobe-lobe interactions, and salt at endosomal pH. J Mol Biol. 2010 Feb 12;396(1):130-40
James, N.G., Ross, J.A., Mason, A.B., and Jameson, D.M., Excited-state lifetime studies of the three tryptophan residues in the N-lobe of human serum transferrin. Protein Sci. 2010 Jan;19(1):99-110
Steere, A.N., Roberts, S.E., Byrne, S.L., Dennis, C.N., Bobst, C.E., Kaltashov, I.A., Smith, V.C., MacGillivray, R.T., and Mason, A.B., Properties of a homogeneous C-lobe prepared by introduction of a TEV cleavage site between the lobes of human transferrin. Protein Expr Purif. 2010 Jul;72(1):32-41
Leverence, R., Mason, A.B., Kaltashov, I.A., Noncanonical interactions between serum transferrin and transferrin receptor evaluated with electrospray ionization mass spectrometry. Proc Natl Acad Sci U S A. 2010 May 4;107(18):8123-8
Yoon, D.J., Kwan, B.H., Chao, F.C., Nicolaides, T.P., Phillips, J.J., Lam, G.Y., Mason, A.B., Weiss, W.A., and Kamei, D.T., Intratumoral therapy of glioblastoma multiforme using genetically engineered transferrin for drug delivery. Cancer Res. 2010 Jun 1;70(11):4520-7
Byrne, S.L., Steere, A.N., Chasteen, N.D., and Mason, A.B., Identification of a kinetically significant anion binding (KISAB) site in the N-lobe of human serum transferrin. Biochemistry. 2010 May 18;49(19):4200-7
* indicates equal contribution
Department of Biochemistry
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