3DNC

Carboxysome shell protein, CcmK2 C-terminal deletion mutant, with a closer spacing between hexamers

Summary for 3DNC

• Entry DOI: 10.2210/pdb3dnc/pdb
• Related: 2A10 2A18 2A1B 3BN4 3CIM 3DN9
• Descriptor: Carbon dioxide-concentrating mechanism protein ccmK homolog 2, SULFATE ION, GLYCEROL, ... (4 entities in total)
• Functional Keywords: hexamer, structural protein
• Biological source: Synechocystis sp.
• Total number of polymer chains: 1
• Total formula weight: 10897.32

Authors

Tanaka, S.,Sawaya, M.R.,Yeates, T.O. (deposition date: 2008-07-01, release date: 2009-01-20, Last modification date: 2023-08-30)

Primary citation

Tanaka, S.,Sawaya, M.R.,Phillips, M.,Yeates, T.O.
Insights from multiple structures of the shell proteins from the beta-carboxysome.
Protein Sci., 18:108-120, 2009

PubMed Abstract: Carboxysomes are primitive bacterial organelles that function as a part of a carbon concentrating mechanism (CCM) under conditions where inorganic carbon is limiting. The carboxysome enhances the efficiency of cellular carbon fixation by encapsulating together carbonic anhydrase and the CO(2)-fixing enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). The carboxysome has a roughly icosahedral shape with an outer shell between 800 and 1500 A in diameter, which is constructed from a few thousand small protein subunits. In the cyanobacterium Synechocystis sp. PCC 6803, the previous structure determination of two homologous shell protein subunits, CcmK2 and CcmK4, elucidated how the outer shell is formed by the tight packing of CcmK hexamers into a molecular layer. Here we describe the crystal structure of the hexameric shell protein CcmK1, along with structures of mutants of both CcmK1 and CcmK2 lacking their sometimes flexible C-terminal tails. Variations in the way hexamers pack into layers are noted, while sulfate ions bound in pores through the layer provide further support for the hypothesis that the pores serve for transport of substrates and products into and out of the carboxysome. One of the new structures provides a high-resolution (1.3 A) framework for subsequent computational studies of molecular transport through the pores. Crystal and solution studies of the C-terminal deletion mutants demonstrate the tendency of the terminal segments to participate in protein--protein interactions, thereby providing a clue as to which side of the molecular layer of hexameric shell proteins is likely to face toward the carboxysome interior.

PubMed: 19177356
DOI: 10.1002/pro.14

Experimental method

X-RAY DIFFRACTION (2.05 Å)