SlyD (accessiton: NP_755987) is a putative folding helper protein from the Escherichia coli cytosol, which has N-terminal prolyl isomerase domain of the FKBP type and a most likely unstructured C-terminal tail. SlyD is an important factor in the biosynthesis of the metal cluster in the [NiFe]-hydrogenase enzymes, and exhibits several activities including that of a peptidyl-prolyl isomerase Synonyms: FKBP-Type Peptidyl-Prolyl Cis-Trans Isomerase, SlyD