The structure of a functional unit from the wall of a gastropod hemocyanin offers a possible mechanism for cooperativity.
Structure-function relationships in a molluscan hemocyanin have been investigated by determining the crystal structure of the Rapana thomasiana (gastropod) hemocyanin functional unit RtH2e in deoxygenated form at 3.38 A resolution. This is the first X-ray structure of an unit from the wall of the molluscan hemocyanin cylinder. The crystal structure of RtH2e demonstrates molecular self-assembly of six identical molecules forming a regular hexameric cylinder. This suggests how the functional units are ordered in the wall of the native molluscan hemocyanins. The molecular arrangement is stabilized by specific protomer-to-protomer interactions, which are probably typical for the functional units building the wall of the cylinders. A molecular mechanism for cooperative dioxygen binding in molluscan hemocyanins is proposed on the basis of the molecular interactions between the protomers. In particular, the deoxygenated RtH2e structure reveals a tunnel leading from two opposite sides of the molecule to the active site. The tunnel represents a possible entrance pathway for dioxygen molecules. No such tunnels have been observed in the crystal structure of the oxy-Odg, a functional unit from the Octopus dofleini (cephalopod) hemocyanin in oxygenated form.
Perbandt
Markus
M
Institute of Biochemistry and Molecular Biology I, University Hospital Hamburg-Eppendorf, c/o DESY, Building 22a, Notkestrasse 85, 22603 Hamburg, Germany.
Guthöhrlein
Eckhart W
EW
Rypniewski
Wojciech
W
Idakieva
Krassimira
K
Stoeva
Stanka
S
Voelter
Wolfgang
W
Genov
Nicolay
N
Betzel
Christian
C
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D018360:Crystallography, X-Ray; D019281:Dimerization; D006031:Glycosylation; D006433:Hemocyanins / Q000737:chemistry* / Q000378:metabolism; D006458:Hemolymph / Q000737:chemistry; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008974:Mollusca; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship
D006433:Hemocyanins; D010100:Oxygen