The Structure of β-Carbonic Anhydrase from the Carboxysomal Shell Reveals a Distinct Subclass with One Active Site for the Price of Two

Authors

Michael R. Sawaya, University of California, Los Angeles
Gordon C. Cannon, University of Southern MississippiFollow
Sabine Heinhorst, University of Southern MississippiFollow
Shiho Tanaka, University of California, Los Angeles
Eric B. Williams, University of Southern MississippiFollow
Todd O. Yeates, University of California, Los Angeles
Cheryl A. Kerfeld, University of California, Los Angeles

Document Type

Article

Publication Date

3-17-2006

Department

Chemistry and Biochemistry

School

Mathematics and Natural Sciences

Abstract

CsoSCA (formerly CsoS3) is a bacterial carbonic anhydrase localized in the shell of a cellular microcompartment called the carboxysome, where it converts HCO^-₃ to CO₂ for use in carbon fixation by ribulose-bisphosphate carboxylase/oxygenase (RuBisCO). CsoSCA lacks significant sequence similarity to any of the four known classes of carbonic anhydrase (α, β, γ, or δ), and so it was initially classified as belonging to a new class, ϵ. The crystal structure of CsoSCA from Halothiobacillus neapolitanus reveals that it is actually a representative member of a new subclass of β-carbonic anhydrases, distinguished by a lack of active site pairing. Whereas a typical β-carbonic anhydrase maintains a pair of active sites organized within a two-fold symmetric homodimer or pair of fused, homologous domains, the two domains in CsoSCA have diverged to the point that only one domain in the pair retains a viable active site. We suggest that this defunct and somewhat diminished domain has evolved a new function, specific to its carboxysomal environment. Despite the level of sequence divergence that separates CsoSCA from the other two subclasses of β-carbonic anhydrases, there is a remarkable level of structural similarity among active site regions, which suggests a common catalytic mechanism for the interconversion of HCO^-₃ and CO₂. Crystal packing analysis suggests that CsoSCA exists within the carboxysome shell either as a homodimer or as extended filaments.

Comments

Publisher Version

Publication Title

Journal of Biological Chemistry

Volume

281

Issue

11

First Page

7546

Last Page

7555

Recommended Citation

Sawaya, M. R., Cannon, G. C., Heinhorst, S., Tanaka, S., Williams, E. B., Yeates, T. O., Kerfeld, C. A. (2006). The Structure of β-Carbonic Anhydrase from the Carboxysomal Shell Reveals a Distinct Subclass with One Active Site for the Price of Two. Journal of Biological Chemistry, 281(11), 7546-7555.
Available at: https://aquila.usm.edu/fac_pubs/9056