1h45: Difference between revisions

==Overview==

The mammalian iron-binding proteins lactoferrin (Lf) and transferrin (Tf), bind iron very tightly, but reversibly. Despite homologous structures and, essentially identical iron binding sites, Tf begins to release iron at pH, 6.0, whereas Lf retains iron to pH approximately 3.5. This difference in, iron retention gives the two proteins different biological roles. Two, lysine residues, Lys 206 and Lys 296, which form a hydrogen-bonded, dilysine pair in human Tf, have been shown to strongly influence iron, release from the N-lobe. The equivalent residues in human Lf are Arg 210, and Lys 301, and we have here mutated Arg 210 in the N-lobe half-molecule, of human lactoferrin, Lf(N), to probe its role in iron release. The Lf(N), mutants R210G, R210E, and R210L were expressed, purified, and, crystallized, and their crystal structures were determined and refined at, resolutions of 1.95 A (R210G), 2.2 A (R210E), and 2.0 A (R210L). The, overall structures are very similar to that of wild-type Lf(N), but with, small differences in domain orientations. In each of the mutants, however, Lys 301 (equivalent to Lys 296 in Tf) changes its conformation to fill the, space occupied by Arg 210 Neta2 in wild-type Lf(N), interacting with the, two tyrosine ligands Tyr 92 and Tyr 192. By comparison with other Lf and, Tf structures, we conclude that Lys 301 (or Lys 296 in Tf) only occupies, this site when residue 210 (206 in Tf) is nonpositive (neutral as in R210G, and R210L or negative as in R210E). Thus, Lys 206 in the Tf dilysine pair, is identified as having a depressed pK(a). Three specific sites are, variably occupied by polar groups in the Lf mutants and other Lf and Tf, proteins, and when coupled with iron-release data, these give new insights, into the factors that most influence iron retention at low pH.

==About this Structure==

[[Category: metal transport]]