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Published May 15, 1996 | Published
Journal Article Open

A Left-handed β Helix Revealed by the Crystal Structure of a Carbonic Anhydrase from the Archaeon Methanosarcina thermophila

Abstract

A carbonic anhydrase from the thermophilic archaeon Methanosarcina thermophila that exhibits no significant sequence similarity to known carbonic anhydrases has recently been characterized. Here we present the structure of this enzyme, which adopts a left-handed parallel β-helix fold. This fold is of particular interest since it contains only left-handed crossover connections between the parallel β-strands, which so far have been observed very infrequently. The active form of the enzyme is a trimer with three zinc-containing active sites, each located at the interface between two monomers. While the arrangement of active site groups differs between this enzyme and the carbonic anhydrases from higher vertebrates, there are structural similarities in the zinc coordination environment, suggestive of convergent evolution dictated by the chemical requirements for catalysis of the same reaction. Based on sequence similarities, the structure of this enzyme is the prototype of a new class of carbonic anhydrases with representatives in all three phylogenetic domains of life.

Additional Information

© 1996 Oxford University Press. Received on November 17, 1995; revised on January 9, 1996. The authors would like to thank Dr Joachim Behlke for carrying out the analytical ultracentrifugation experiments. This work was supported by Deutsche Forschungsgemeinschaft postdoctoral fellowships (to C.K. and H.S.), by USPHS and NSF grants (to D.C.R.) and by an NIH grant (to J.G.F.). The rotation camera facility at SSRL is supported by DOE and NIH. Coordinates have been deposited in the Protein Data Bank PDBID code ITHJ, they can also be requested by E-mail to kisker@citray.caltech.edu.

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