For chem791A Jmol presentation Human Serum Transferrin N-Lobe (click on the "About" menu above for more info on Jmol).

Transferrins comprise a class of monomeric glycoproteins found in all vertebrates, whose function is iron sequestration and transport. The two lobes of the protein (commonly referred to as and C-lobes) have a very high degree of structural identity.

Each lobe has one binding site for Human serum transferrin can also bind other nonferrous metals.(indium, gallium and bismuth etc.)

What is holding this conformation? (other than hydrophobic effect and H-bonds)

The beta sheet is a mixture of antiparallel- and parallel-beta sheets, they form two alpha/beta domain

Even though the of the protein is buried inside, there are still exposed to solvent. Why is that? Because those are for interaction between hTf two lobes and between hTf and TfR.

Human serum transferrin (hTf) provides a major route for delivery of otherwise insoluble iron to cells via a receptor-mediated endocytosis. Only the diferric form of hTf binds to the receptor (TfR) at the cell surface. For , it interacts with a helical domain in TfR. For , it interacts with the protease-like domain in TfR.

If we take a on N-lobe binding site, it is a parallal beta-sheet connected by alpha-helices.

Presentation by Mingxuan Zhang, Department of Chemistry, University of Massachusetts. Dec. 1, 2004.

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ABSTRACT:
Regulatory factor X (RFX) proteins are transcriptional activators that recognize X-boxes (DNA of the sequence 5'-GTNRCC(0-3N)RGYAAC-3', where N is any nucleotide, R is a purine and Y is a pyrimidine) using a highly conserved 76-residue DNA-binding domain (DBD). DNA-binding defects in the protein RFX5 cause bare lymphocyte syndrome or major histocompatibility antigen class II deficiency. RFX1, -2 and -3 regulate expression of other medically important gene products (for example, interleukin-5 receptor alpha chain, IL-5R alpha). Fusions of the ligand-binding domain of the oestrogen receptor with the DBD of RFX4 occur in some human breast tumours. Here we present a 1.5 A-resolution structure of two copies of the DBD of human RFX1 (hRFX1) binding cooperatively to a symmetrical X-box. hRFX1 is an unusual member of the winged-helix subfamily of helix-turn-helix proteins because it uses a beta-hairpin (or wing) to recognize DNA instead of the recognition helix typical of helix-turn-helix proteins. A new model for interactions between linker histones and DNA is proposed.