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Journal of Bacteriology, October 1999, p. 6247-6253, Vol. 181, No. 20
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

A Plant-Type (beta -Class) Carbonic Anhydrase in the Thermophilic Methanoarchaeon Methanobacterium thermoautotrophicum

Kerry S. Smith and James G. Ferry*

Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802

Received 21 April 1999/Accepted 30 July 1999

Carbonic anhydrase, a zinc enzyme catalyzing the interconversion of carbon dioxide and bicarbonate, is nearly ubiquitous in the tissues of highly evolved eukaryotes. Here we report on the first known plant-type (beta -class) carbonic anhydrase in the archaea. The Methanobacterium thermoautotrophicum Delta H cab gene was hyperexpressed in Escherichia coli, and the heterologously produced protein was purified 13-fold to apparent homogeneity. The enzyme, designated Cab, is thermostable at temperatures up to 75°C. No esterase activity was detected with p-phenylacetate as the substrate. The enzyme is an apparent tetramer containing approximately one zinc per subunit, as determined by plasma emission spectroscopy. Cab has a CO2 hydration activity with a kcat of 1.7 × 104 s-1 and Km for CO2 of 2.9 mM at pH 8.5 and 25°C. Western blot analysis indicates that Cab (beta  class) is expressed in M. thermoautotrophicum; moreover, a protein cross-reacting to antiserum raised against the gamma  carbonic anhydrase from Methanosarcina thermophila was detected. These results show that beta -class carbonic anhydrases extend not only into the Archaea domain but also into the thermophilic prokaryotes.

* Corresponding author. Mailing address: Department of Biochemistry and Molecular Biology, 205 South Frear Laboratory, The Pennsylvania State University, University Park, PA 16802. Phone: (814) 863-5721. Fax: (814) 863-6217. E-mail: jgf3{at}psu.edu.

Journal of Bacteriology, October 1999, p. 6247-6253, Vol. 181, No. 20
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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