1.8 A crystal structure of the C-terminal domain of rabbit serum haemopexin.
BACKGROUND
Haemopexin is a serum glycoprotein that binds haem reversibly and delivers it to the liver where it is taken up by receptor-mediated endocytosis. Haemopexin has two homologous domains, each having a characteristic fourfold internal sequence repeat. Haemopexin-type domains are also found in other proteins, including the serum adhesion protein vitronectin and various collagenases, in which they mediate protein-protein interactions.


RESULTS
We have determined the crystal structure of the C-terminal domain of haemopexin at 1.8 A resolution. The domain is folded into four beta-leaflet modules, arranged in succession around a central pseudo-fourfold axis. A funnel-shaped tunnel through the centre of this disc-shaped domain serves as an ion-binding site.


CONCLUSIONS
A model for haem binding by haemopexin is proposed, utilizing an anion-binding site at the wider end of the central tunnel, together with an associated cleft. This parallels the active-site location in other beta-propeller structures. The capacity to bind both cations and anions, together with the disc shape of the domain, suggests that such domains may be used widely for macromolecular recognition.
Faber
H R
HR
Department of Chemistry and Biochemistry, Massey University, Palmerston North, New Zealand.
Groom
C R
CR
Baker
H M
HM
Morgan
W T
WT
Smith
A
A
Baker
E N
EN
D000595:Amino Acid Sequence; D000818:Animals; D000838:Anions / Q000378:metabolism; D018360:Crystallography, X-Ray; D006418:Heme / Q000378:metabolism; D006466:Hemopexin / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D008670:Metals / Q000378:metabolism; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011817:Rabbits; D017386:Sequence Homology, Amino Acid
D000838:Anions; D008670:Metals; D006418:Heme; D006466:Hemopexin