The three-dimensional structure of a form of human apolactoferrin, in which one lobe (the N-lobe) has an open conformation and the other lobe (the C-lobe) is closed, has been refined at 2.0 A resolution. The refinement, by restrained least-squares methods, used synchrotron radiation X-ray diffraction data combined with a lower resolution diffractometer data set ...
The three-dimensional structure of a form of human apolactoferrin, in which one lobe (the N-lobe) has an open conformation and the other lobe (the C-lobe) is closed, has been refined at 2.0 A resolution. The refinement, by restrained least-squares methods, used synchrotron radiation X-ray diffraction data combined with a lower resolution diffractometer data set. The final refined model (5346 protein atoms from residues 1-691, two Cl- ions and 363 water molecules) gives a crystallographic R factor of 0.201 (Rfree = 0. 286) for all 51305 reflections in the resolution range 10.0-2.0 A. The conformational change in the N-lobe, which opens up the binding cleft, involves a 54 degrees rotation of the N2 domain relative to the N1 domain. This also results in a small reorientation of the two lobes relative to one another with a further approximately 730 A2 of surface area being buried as the N2 domain contacts the C-lobe and the inter-lobe helix. These new contacts also involve the C-terminal helix and provide a mechanism through which the conformational and iron-binding status of the N-lobe can be signalled to the C-lobe. Surface-area calculations indicate a fine balance between open and closed forms of lactoferrin, which both have essentially the same solvent-accessible surface. Chloride ions are bound in the anion-binding sites of both lobes, emphasizing the functional significance of these sites. The closed configuration of the C-lobe, attributed in part to weak stabilization by crystal packing interactions, has important implications for lactoferrin dynamics. It shows that a stable closed structure, essentially identical to that of the iron-bound form, can be formed in the absence of iron binding.
Structure of human lactoferrin: crystallographic structure analysis and refinement at 2.8 A resolution. Anderson, B.F., Baker, H.M., Norris, G.E., Rice, D.W., Baker, E.N. (1989) J Mol Biol 209: 711
Transferrins: Insights Into Structure and Function from Studies on Lactoferrin Baker, E.N., Rumball, S.V., Anderson, B.F. (1987) Trends Biochem Sci 12: 350
Structure of human lactoferrin at 3.2-A resolution. Anderson, B.F., Baker, H.M., Dodson, E.J., Norris, G.E., Rumball, S.V., Waters, J.M., Baker, E.N. (1987) Proc Natl Acad Sci U S A 84: 1769
Organizational Affiliation:
Department of Chemistry, Massey University, Palmerston North, New Zealand.
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