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  • Title: The structure of a functional unit from the wall of a gastropod hemocyanin offers a possible mechanism for cooperativity.
    Author: Perbandt M, Guthöhrlein EW, Rypniewski W, Idakieva K, Stoeva S, Voelter W, Genov N, Betzel C.
    Journal: Biochemistry; 2003 Jun 03; 42(21):6341-6. PubMed ID: 12767214.
    Abstract:
    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.
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