title: The structures of the PII proteins from the cyanobacteria Synechococcus sp. PCC 7942 and Synechocystis sp. PCC 6803.
abstract: The PII proteins from the cyanobacteria Synechococcus sp. PCC 7942 and Synechocystis sp. PCC 6803 have been crystallized and high-resolution structures have been obtained using X-ray crystallography. The core of these new structures is similar to that of the PII proteins from Escherichia coli, although the structures of the T- and C-loops differ. The T-loop of the Synechococcus protein is ordered, but appears to be stabilized by crystal contacts. The same loop in the Synechocystis protein is disordered. The C-terminus of the Synechocystis protein is stabilized by hydrogen bonding to the same region of a crystallographically related molecule. The same terminus in the Synechococcus protein is stabilized by coordination with a metal ion. These observations are consistent with the idea that both the T-loop and the C-terminus of PII proteins are flexible in solution and that this flexibility may be important for receptor recognition. Sequence comparisons are used to identify regions of the sequence unique to the cyanobacteria.
authors.affiliation: Department of Biochemistry and Molecular Biology, James Cook University, Townsville, Queensland 4811, Australia.
authors.forename: Yibin
authors.initials: Y
authors.lastname: Xu
authors.forename: Paul D
authors.initials: PD
authors.lastname: Carr
authors.forename: Paula
authors.initials: P
authors.lastname: Clancy
authors.forename: Mario
authors.initials: M
authors.lastname: Garcia-Dominguez
authors.forename: Karl
authors.initials: K
authors.lastname: Forchhammer
authors.forename: Francisco
authors.initials: F
authors.lastname: Florencio
authors.forename: Subhash G
authors.initials: SG
authors.lastname: Vasudevan
authors.forename: Nicole
authors.initials: N
authors.lastname: Tandeau de Marsac
authors.forename: David L
authors.initials: DL
authors.lastname: Ollis
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000737:chemistry* / Q000235:genetics; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009532:Nickel / Q000737:chemistry / Q000378:metabolism; D051922:PII Nitrogen Regulatory Proteins; D011487:Protein Conformation; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D051922:PII Nitrogen Regulatory Proteins; C404143:PIID regulatory protein, Bacteria; D009532:Nickel; D002118:Calcium