Crystal Structure of Halophilic Dodecin: A Novel, Dodecameric Flavin Binding Protein from Halobacterium salinarum
Archaea obtained their name from their natural habitat, which reminds of the early earth surface. Among the extreme phenotypes within these entity, halophilic archaea exhibit adaption to high salt environment. Consequently these organisms are found under salt concentrations where they have to keep the osmolar balance by an salt-in-strategy. The uptake of salt in high amounts forces basic strategies of the cellular components to resist this otherwise denaturing environment.
Dodecin is a dodecameric, hollow-sphere arranged flavoprotein in the cytosol of Halobacterium salinarum. A single protein consists of 68 amino acid residues representing the smallest flavoprotein known to date. Of particular structural interest is the aromatic tetrade, which contains two π-stacked flavins covered by two tryptophans of the adjacent monomers.
Of particular structural interest is the aromatic tetrade, which contains two π-stacked flavins covered by two tryptophans of the adjacent monomers.
The binding motif, allowing α-stacking interaction within this aromatic tetrade, is unique in the world of proteins and a radical deviation of all flavin binding mechanisms known to date. Dodecin binds its cofactor in a fundamentally different manner via the isoalloxazine ring. This structural particularity raises the question as to a functional potential, which is interesting with respect to the wide range of functions flavoproteins can perform. In addition, the character of π-stacking in this sandwich-like arrangement implies a high substrate tolerance of this binding type. The protein envelope may be able to readily accommodate other aromatic systems which are similar to the tricyclic isoalloazine ring and has led to the idea that dodecin may act as a kind of shuttle system for biological active compounds.
B. Bieger, L.-O. Essen, D. Oesterhelt, Structure, 2003, 11, 375-385