Biological Assembly 1  

 3D View: Structure | Electron Density | Ligand Interaction

Global Symmetry: Asymmetric - C1 
Global Stoichiometry: Monomer - A1 

Biological assembly 1 assigned by authors and generated by PISA (software)

Macromolecule Content

• Total Structure Weight: 75.65 kDa 
• Atom Count: 5103 
• Residue Count: 673 
• Unique protein chains: 1

6CTC

Crystal structure of human transferrin bound to Triferic FPC iron pyrophosphate

• DOI: 10.2210/pdb6CTC/pdb

• Classification: METAL TRANSPORT
• Organism(s): Homo sapiens
• Expression System: Homo sapiens
• Mutation(s): No 


• Deposited: 2018-03-22 Released: 2018-10-24 
• Deposition Author(s): Edwards, T.E., Pratt, R.

---

Experimental Data Snapshot

• Method: X-RAY DIFFRACTION
• Resolution: 2.60 Å
• R-Value Free: 0.253 
• R-Value Work: 0.180 
• R-Value Observed: 0.184 

Literature

Ferric pyrophosphate citrate: interactions with transferrin.

Pratt, R., Handelman, G.J., Edwards, T.E., Gupta, A.

(2018) Biometals 31: 1081-1089

• PubMed: 30311019 
• DOI: 10.1007/s10534-018-0142-2
• Primary Citation of Related Structures:  
  6CTC


• PubMed Abstract: 
  

There are several options available for intravenous application of iron supplements, but they all have a similar structure:-an iron core surrounded by a carbohydrate coating. These nanoparticles require processing by the reticuloendothelial system to release iron, which is subsequently picked up by the iron-binding protein transferrin and distributed throughout the body, with most of the iron supplied to the bone marrow. This process risks exposing cells and tissues to free iron, which is potentially toxic due to its high redox activity. A new parenteral iron formation, ferric pyrophosphate citrate (FPC), has a novel structure that differs from conventional intravenous iron formulations, consisting of an iron atom complexed to one pyrophosphate and two citrate anions. In this study, we show that FPC can directly transfer iron to apo-transferrin. Kinetic analyses reveal that FPC donates iron to apo-transferrin with fast binding kinetics. In addition, the crystal structure of transferrin bound to FPC shows that FPC can donate iron to both iron-binding sites found within the transferrin structure. Examination of the iron-binding sites demonstrates that the iron atoms in both sites are fully encapsulated, forming bonds with amino acid side chains in the protein as well as pyrophosphate and carbonate anions. Taken together, these data demonstrate that, unlike intravenous iron formulations, FPC can directly and rapidly donate iron to transferrin in a manner that does not expose cells and tissues to the damaging effects of free, redox-active iron.

---

Organizational Affiliation: 

University of California Irvine, Orange, CA, USA.

Macromolecules

Entity ID: 1
Molecule	Chains	Sequence Length	Organism	Details	Image
Serotransferrin	A	679	Homo sapiens	Mutation(s): 0  Gene Names: TF, PRO1400
Find proteins for P02787 (Homo sapiens) Explore P02787  Go to UniProtKB:  P02787
NIH Common Fund Data Resources
PHAROS:  P02787 GTEx:  ENSG00000091513

Small Molecules

Ligands 3 Unique
ID	Chains	Name / Formula / InChI Key	2D Diagram
POP	A	PYROPHOSPHATE 2- H2 O7 P2 XPPKVPWEQAFLFU-UHFFFAOYSA-L
CO3	A	CARBONATE ION C O3 BVKZGUZCCUSVTD-UHFFFAOYSA-L
FE	A	FE (III) ION Fe VTLYFUHAOXGGBS-UHFFFAOYSA-N

Experimental Data & Validation

Experimental Data

• Method: X-RAY DIFFRACTION
• Resolution: 2.60 Å
• R-Value Free: 0.253 
• R-Value Work: 0.180 
• R-Value Observed: 0.184 
• Space Group: P 2₁ 2₁ 2₁

Unit Cell:

Length ( Å )	Angle ( ˚ )
a = 74.37	α = 90
b = 90.16	β = 90
c = 110.43	γ = 90

Software Package:

Software Name	Purpose
XDS	data reduction
XSCALE	data scaling
PHASER	phasing
PHENIX	refinement
PDB_EXTRACT	data extraction

Structure Validation

Entry History 

Deposition Data

• Deposited Date: 2018-03-22 
• Released Date: 2018-10-24 
Deposition Author(s): Edwards, T.E., Pratt, R.

Revision History 

• Version 1.0: 2018-10-24
  Type: Initial release
  
• Version 1.1: 2018-11-28
  Changes: Data collection, Database references