title: Expression and characterization of a heterodimer of Streptomyces chromofuscus phospholipase D.
abstract: Streptomyces chromofuscus phospholipase D (PLD) is secreted by the bacterium and proteolytically cleaved to a more active form (PLD(37/18)) where the two parts of the molecule are still tightly associated. Based on previous sequencing results of authentic PLD(37/18), we have constructed a vector consisting of separate ORFs for the N-terminal and C-terminal portions of S. chromofuscus PLD and overexpressed active heterodimeric PLD. Neither fragment cloned separately folded properly. The identity of each peptide was confirmed by peptide-mass fingerprinting with MALDI-TOF mass spectrometry. The recombinant complex had a specific activity about six times higher than that of the recombinant intact PLD enzyme and was no longer activated by phosphatidic acid (PA). Phosphotransferase activity, binding affinity to phospholipid vesicles, loss of product activation, pH profile and pH-related Ca(2+) activation and inhibition were comparable to authentic PLD(37/18) purified from S. chromofuscus growth medium. PLD(37) alone could also be isolated; the enzyme was active but not as stable as PLD(37/18). These experimental results strongly support the hypothesis that the C-terminal peptide is necessary for correct folding and insertion of catalytic metal ions. However, they suggest the ligands involved in Fe(3+) coordination must be altered upon cleavage of the protein. Asp389, in the C-terminal fragment, whose replacement impairs Fe(3+) binding to the protein, must be replaced by another ligand, since the N-terminal fragment, once folded, is active. In the process of cloning the two peptides, the complete signal sequence for this protein was also determined. The signal peptide of S. chromofuscus PLD enzyme contained a twin arginine motif suggesting that S. chromofuscus PLD, like Bacillus subtilis phoD, is most likely secreted by the TAT translocation pathway under the transcriptional control of the pho regulon.
authors.affiliation: Merkert Chemistry Center, Boston College, 2609 Beacon Street, Chestnut Hill, MA 02167, USA.
authors.forename: Hongying
authors.initials: H
authors.lastname: Yang
authors.forename: Mary F
authors.initials: MF
authors.lastname: Roberts
mesh_terms: D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D019281:Dimerization; D004533:Egtazic Acid / Q000494:pharmacology; D004795:Enzyme Stability; D005822:Genetic Vectors; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008081:Liposomes / Q000378:metabolism; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D016366:Open Reading Frames; D010449:Peptide Mapping; D010739:Phospholipase D / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D010770:Phosphotransferases / Q000378:metabolism; D017510:Protein Folding; D021382:Protein Sorting Signals / Q000187:drug effects; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013302:Streptomyces / Q000201:enzymology*; D013379:Substrate Specificity; D014357:Trypsin / Q000494:pharmacology
chemical_list: D008081:Liposomes; D021382:Protein Sorting Signals; D011994:Recombinant Proteins; D004533:Egtazic Acid; D010770:Phosphotransferases; D010739:Phospholipase D; D014357:Trypsin