Journal:JBIC:14

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

Tianfan Cheng, Hongyan Li, Wei Xia and Hongzhe Sun^[1]

Molecular Tour
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, 2kr7). HpSlyDΔC folds into two well-separated, orientation-independent domains: the PPIase-active FKBP domain (in cyan) and the chaperone-active insert-in-flap (IF) domain (in red), linkers are in darkmagenta. 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 (residues experiencing relatively large chemical shift perturbations upon interactions of HpSlyDΔC with Ni²⁺ are in blueviolet). The twin-arginine translocation (Tat) signal peptide from the small subunit of [NiFe] hydrogenase (HydA) binds the protein at the IF domain (residues in orange). Surprisingly, several residues (Ile41, Gly42, Ile46, and Asn31) were from the FKBP domain, which is likely due to the binding of the longer n-region of HydA Tat peptide to the FKBP domain. Nickel binding and the recognition of the Tat signal peptide by the protein suggest that SlyD participates in [NiFe] hydrogenase maturation processes.

PDB reference: solution structure of Helicobacter pylori SlyD, 2kr7.