PDBsum entry 2a1b

Carboxysome

PDB id: 2a1b

Contents

Protein chains

(+ 6 more) 101 a.a. *

* Residue conservation analysis

PDB id:

2a1b

Name:

Carboxysome

Title:

Carboxysome shell protein ccmk2

Structure:

Carbon dioxide concentrating mechanism protein ccmk homolog 2. Chain: a, b, c, d, e, f, g, h, i, j, k, l. Synonym: ccmk2. Engineered: yes. Mutation: yes

Source:

Synechocystis sp.. Organism_taxid: 1148. Strain: pcc 6803. Gene: ccmk2. Expressed in: escherichia coli. Expression_system_taxid: 562.

Biol. unit:

Hexamer (from PQS)

Resolution:

2.90Å R-factor: 0.313 R-free: 0.346

Authors:

C.A.Kerfeld,M.R.Sawaya,S.Tanaka,C.V.Nguyen,M.Phillips,M.Beeby, T.O.Yeates

Key ref:

C.A.Kerfeld et al. (2005). Protein structures forming the shell of primitive bacterial organelles. Science, 309, 936-938. PubMed id: 16081736 DOI: 10.1126/science.1113397

Date:

20-Jun-05 Release date: 09-Aug-05

Protein chains

P72761  (CCMK2_SYNY3) -  Carboxysome shell protein CcmK2 from Synechocystis sp. (strain PCC 6803 / Kazusa)

Seq: 103 a.a.

Struc: 101 a.a.*

* PDB and UniProt seqs differ at 1 residue position (black cross)

DOI no: 10.1126/science.1113397

Science 309:936-938 (2005)

PubMed id: 16081736

Protein structures forming the shell of primitive bacterial organelles.

C.A.Kerfeld, M.R.Sawaya, S.Tanaka, C.V.Nguyen, M.Phillips, M.Beeby, T.O.Yeates.

ABSTRACT

Bacterial microcompartments are primitive organelles composed entirely of protein subunits. Genomic sequence databases reveal the widespread occurrence of microcompartments across diverse microbes. The prototypical bacterial microcompartment is the carboxysome, a protein shell for sequestering carbon fixation reactions. We report three-dimensional crystal structures of multiple carboxysome shell proteins, revealing a hexameric unit as the basic microcompartment building block and showing how these hexamers assemble to form flat facets of the polyhedral shell. The structures suggest how molecular transport across the shell may be controlled and how structural variations might govern the assembly and architecture of these subcellular compartments.

Selected figure(s)

Figure 3.
Fig. 3. (A) The three-dimensional crystal structure of BMC domain protein, CcmK4, determined at a resolution of 1.8 Å. (B) The concave surface of the CcmK4 hexamer. CcmK4 monomers are colored alternately blue and gray, with all six C termini in green. Also shown is the CcmK2 C terminus (red) in its corresponding position after a superposition of CcmK2 and CcmK4 hexamers. The superposition (not shown) indicates that the backbones of the two hexamers are nearly identical up to residues Pro97 (CcmK4)/Glu95 (CcmK2). The structural differences at the C termini (labeled) suggest one reason why CcmK4 packing is limited to chains of hexamers. In CcmK4, the C termini extend outward, toward the corners of the hexamer. These are the positions where three hexamers meet in the CcmK2 sheet but not in the CcmK4 structures. (C and D) A close-up view of the pores (concave side) formed at the six-fold axis of symmetry in the CcmK2 (C) and CcmK4 (D) hexamers. The surfaces are colored according to electrostatic potential, with blue positive and red negative. Positively charged, conserved amino acid side chains lining the pore are highlighted (Lys36 in CcmK2, Arg38 in CcmK4). This figure and Fig. 4 were illustrated with PyMOL (32).

Figure 4.
Fig. 4. Crystal packing of BMC domain proteins in molecular layers. (A) CcmK2 hexamers packed in uniform orientations (convex face shown). (B) CcmK4 hexamers (crystal form 2) packed in strips of alternating orientation. In the side view of each sheet, arrows mark the positions of the pores.

The above figures are reprinted by permission from the AAAs: Science (2005, 309, 936-938) copyright 2005.

Figures were selected by an automated process.