Journal:JBIC:14

<StructureSection load='2kr7' size='500' side='right' scene='Journal:JBIC:14/Cv/2' caption=''>

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 <scene name='Journal:JBIC:14/Cv/3'>C-terminus-truncated SlyD</scene> from ''Helicobacter pylori'' (HpSlyDΔC). HpSlyDΔC folds into <scene name='Journal:JBIC:14/Cv/4'>two well-separated, orientation-independent domains:</scene> the <span style="color:cyan;background-color:black;font-weight:bold;">PPIase-active FKBP domain (in cyan)</span> and the <font color='red'><b>chaperone-active insert-in-flap (IF) domain (in red)</b></font>, <font color='darkmagenta'><b>linkers are in darkmagenta</b></font>. The FKBP domain consists of a four-stranded antiparallel <scene name='Journal:JBIC:14/Cv/5'>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.</scene> 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 <scene name='Journal:JBIC:14/Cv/6'>active sites of the FKBP domain, implicating a regulatory role of nickel</scene> <font color='blueviolet'><b>(residues experiencing relatively large chemical shift perturbations upon interactions of HpSlyDΔC with Ni²⁺ are in blueviolet)</b></font>. <scene name='Journal:JBIC:14/Cv/7'>The twin-arginine translocation (Tat) signal peptide from the small subunit of [NiFe] hydrogenase (HydA) binds the protein at the IF domain</scene> <font color='orange'><b>(residues in orange)</b></font>. 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.