Multifaceted SlyD from Helicobacter pylori: implication in [NiFe] hydrogenase maturation

SlyD belongs to the FK506-binding protein (FKBP) family with both peptidylprolyl isomerase (PPIase) and chaperone activities, and is considered to be a ubiquitous cytosolic protein-folding facilitator in bacteria. It possesses a histidine- and cysteine-rich C-terminus binding to selected divalent metal ions (e.g., Ni2+, Zn2+), which is important for its involvement in the maturation processes of metalloenzymes. We have determined the solution structure of C-terminus-truncated SlyD from Helicobacter pylori (HpSlyDΔC). HpSlyDΔC folds into two well-separated, orientation-independent domains: the PPIase-active FKBP domain and the chaperone-active insert-in-flap (IF) domain. The FKBP domain consists of a four-stranded antiparallel β-sheet with an α-helix on one side, whereas the IF domain folds into a four-stranded antiparallel β-sheet accompanied by a short α-helix. Intact H. pylori SlyD binds both Ni2+ and Zn2+, with dissociation constants of 2.74 and 3.79 μM respectively. Intriguingly, binding of Ni2+ instead of Zn2+ induces protein conformational changes around the active sites of the FKBP domain, implicating a regulatory role of nickel. The twin-arginine translocation (Tat) signal peptide from the small subunit of [NiFe] hydrogenase (HydA) binds the protein at the IF domain. Nickel binding and the recognition of the Tat signal peptide by the protein suggest that SlyD participates in [NiFe] hydrogenase maturation processes

The Crystal Structure of a Bis(2,6-pyridinedicarboxylato)Chromate(III) Anion with an Elaborate Network of Hydrogen Bonding and Pi Stacking

The synthesis, X-ray crystallography, spectroscopic, and electrochemical properties of the title compound, [Hdpa][Cr(dipic)2]·3H2O, 1, are reported. Compound 1 crystallized in the triclinic space group P-1 with a = 7.1057(11) Å, b = 12.965(2) Å, c = 14.269(2) Å, α = 80.306(3)°, β = 82.101(2)°, γ = 83.799(2)°, and V = 1278.6(4) Å3 with Z = 2. The distorted octahedral chromium anions are part of an elaborate network of hydrogen bonding formed by the waters of solvation, the anion, and cation as well as π-stacking interactions