PDBsum entry 2o7u

Metal transport

PDB id: 2o7u

Contents

Protein chain

(+ 3 more) 329 a.a. *

Ligands

CO3 ×9

Metals

_FE ×9

Waters ×72

* Residue conservation analysis

PDB id:

2o7u

Name:

Metal transport

Title:

Crystal structure of k206e/k296e mutant of the n-terminal half molecule of human transferrin

Structure:

Serotransferrin. Chain: b, a, c, d, e, f, g, h, i. Fragment: n-lobe. Synonym: transferrin, siderophilin, beta-1-metal-binding globulin. Engineered: yes. Mutation: yes

Source:

Homo sapiens. Human. Organism_taxid: 9606. Expressed in: mesocricetus auratus. Expression_system_taxid: 10036. Expression_system_cell_line: bhk. Expression_system_organ: kidney.

Resolution:

2.80Å R-factor: 0.231 R-free: 0.259

Authors:

H.M.Baker,D.Nurizzo,A.B.Mason,E.N.Baker

Key ref:

H.M.Baker et al. (2007). Structures of two mutants that probe the role in iron release of the dilysine pair in the N-lobe of human transferrin. Acta Crystallogr D Biol Crystallogr, 63, 408-414. PubMed id: 17327678 DOI: 10.1107/S0907444907000182

Date:

11-Dec-06 Release date: 23-Jan-07

Protein chains

P02787  (TRFE_HUMAN) -  Serotransferrin from Homo sapiens

Seq: 698 a.a.

Struc: 329 a.a.*

* PDB and UniProt seqs differ at 2 residue positions (black crosses)

DOI no: 10.1107/S0907444907000182

Acta Crystallogr D Biol Crystallogr 63:408-414 (2007)

PubMed id: 17327678

Structures of two mutants that probe the role in iron release of the dilysine pair in the N-lobe of human transferrin.

H.M.Baker, D.Nurizzo, A.B.Mason, E.N.Baker.

ABSTRACT

Iron uptake by humans depends on the ability of the serum protein transferrin (Tf) to bind iron as Fe(3+) with high affinity but reversibly. Iron release into cells occurs through receptor-mediated endocytosis, aided by the lower endosomal pH of about 5.5. The protonation of a hydrogen-bonded pair of lysines, Lys206 and Lys296, adjacent to the N-lobe iron site of Tf has been proposed to create a repulsive interaction that stimulates domain opening and iron release. The crystal structures of two mutants, K206E (in which Lys206 is mutated to Glu) and K206E/K296E (in which both lysines are mutated to Glu), have been determined. The K206E structure (2.6 A resolution; R = 0.213, R(free) = 0.269) shows that a salt bridge is formed between Glu206 and Lys296, thus explaining the drastically slower iron release by this mutant. The K206E/K296E double-mutant structure (2.8 A resolution; R = 0.232, R(free) = 0.259) shows that the Glu296 side chain moves away from Glu206, easing any repulsive interaction and instead interacting with the iron ligand His249. The evident conformational flexibility is consistent with an alternative model for the operation of the dilysine pair in iron release in which it facilitates concerted proton transfer to the tyrosine ligand Tyr188 as one step in the weakening of iron binding.

Selected figure(s)

Figure 1.
Figure 1 Dilysine interaction in the N-lobe of transferrin. (a) Ribbon diagram showing the approach of Lys296 from domain N1 (lower) to Lys206 from domain N2 (upper) adjacent to the bound Fe atom (red sphere). (b) Interactions made by the -amino group of Lys296: hydrogen bonds (broken lines) to Lys206 N^ , Tyr188 O^ and the aromatic ring of Tyr95. This and the other figures were prepared using PyMOL (DeLano, 2002[DeLano, W. L. (2002). The PyMOL Molecular Graphics System. http://www.pymol.org/ .]).

Figure 3.
Figure 3 Mutation site in the K206E/K296E double mutant. (a) Bias-removed OMIT density (F[o] - F[c], contoured at 3 ) for the mutated residues. (b) Side chains of Glu206 and Glu296 in the mutant structure, shown in gold, superimposed on Lys206 and Lys296 in the wild-type structure, shown in silver. Other residues common to both proteins are shown in green with atoms coloured by type. Hydrogen bonds are shown as broken lines and covalent metal-ligand bonds as solid black lines.

The above figures are reprinted by permission from the IUCr: Acta Crystallogr D Biol Crystallogr (2007, 63, 408-414) copyright 2007.

Figures were selected by the author.