Atomic-level models of the bacterial carboxysome shell

Department of Chemistry and Biochemistry, University of California at Los Angeles (UCLA), Los Angeles, CA 90095, USA.
Science (Impact Factor: 33.61). 03/2008; 319(5866):1083-6. DOI: 10.1126/science.1151458
Source: PubMed


The carboxysome is a bacterial microcompartment that functions as a simple organelle by sequestering enzymes involved in carbon
fixation. The carboxysome shell is roughly 800 to 1400 angstroms in diameter and is assembled from several thousand protein
subunits. Previous studies have revealed the three-dimensional structures of hexameric carboxysome shell proteins, which self-assemble
into molecular layers that most likely constitute the facets of the polyhedral shell. Here, we report the three-dimensional
structures of two proteins of previously unknown function, CcmL and OrfA (or CsoS4A), from the two known classes of carboxysomes,
at resolutions of 2.4 and 2.15 angstroms. Both proteins assemble to form pentameric structures whose size and shape are compatible
with formation of vertices in an icosahedral shell. Combining these pentamers with the hexamers previously elucidated gives
two plausible, preliminary atomic models for the carboxysome shell.

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