Isolation and Characterization of the Prochlorococcus Carboxysome Reveal the Presence of the Novel Shell Protein CsoS1D

Document Type

Article

Publication Date

2-1-2012

Department

Chemistry and Biochemistry

School

Mathematics and Natural Sciences

Abstract

Cyanobacteria, including members of the genus Prochlorococcus, contain icosahedral protein microcompartments known as carboxysomes that encapsulate multiple copies of the CO2-fixing enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) in a thin protein shell that enhances the catalytic performance of the enzyme in part through the action of a shell-associated carbonic anhydrase. However, the exact mechanism by which compartmentation provides a catalytic advantage to the enzyme is not known. Complicating the study of cyanobacterial carboxysomes has been the inability to obtain homogeneous carboxysome preparations. This study describes the first successful purification and characterization of carboxysomes from the marine cyanobacterium Prochlorococcus marinus MED4. Because the isolated P. marinus MED4 carboxysomes were free from contaminating membrane proteins, their protein complement could be assessed. In addition to the expected shell proteins, the CsoS1D protein that is not encoded by the canonical cso gene clusters of α-cyanobacteria was found to be a low-abundance shell component. This finding and supporting comparative genomic evidence have important implications for carboxysome composition, structure, and function. Our study indicates that carboxysome composition is probably more complex than was previously assumed based on the gene complements of the classical cso gene clusters.

Publication Title

Journal of Bacteriology

Volume

194

Issue

4

First Page

787

Last Page

795

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