Lemon protein disulfide isomerase: cDNA cloning and biochemical characterization

BACKGROUND: Protein disulfide isomerases (PDIs), a family of structurally related enzymes, aid in protein folding by catalyzing disulfide bonds formation, breakage, or isomerization in newly synthesized proteins and thus. RESULTS: A ClPDI cDNA (1828 bp, GenBank accession HM641784) encoding a putative PDI from Citrus limonum was cloned by polymerase chain reaction (PCR). The DNA sequence encodes a protein of 500 amino acids with a calculated molecular mass of 60.5 kDa. The deduced amino acid sequence is conserved among the reported PDIs. A 3-D structural model of the ClPDI has been created based on the known crystal structure of Homo sapiens (PDB ID: 3F8U_A). The enzyme has two putative active sites comprising the redox-active disulfides between residues 60–63 and 405–408 (motif CGHC). To further characterize the ClPDI, the coding region was subcloned into an expression vector pET-20b (+), transformed into E. coli Rosetta (DE3)pLysS, and recombinant protein expressed. The recombinant ClPDI was purified by a nickel Sepharose column. PDI’s activity was assayed based on the ability of the enzyme to isomerize scrambled RNase A (sRNase A) to active enzyme. The K(M), k(cat) and k(cat)/K(M) values were 8.3 × 10(-3) μM, 3.0 × 10(-5) min(-1), and 3.6 × 10(-1) min(-1) mM(-1). The enzyme was most active at pH 8. CONCLUSIONS: The advantage of this enzyme over the PDI from all other sources is its low K(M). The potential applications of this PDI in health and beauty may worth pursuing. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/1999-3110-54-34) contains supplementary material, which is available to authorized users.