title: Autoproteolytic Activation of a Symbiosis-regulated Truffle Phospholipase A2.
abstract: Fungal phospholipases are members of the fungal/bacterial group XIV secreted phospholipases A(2) (sPLA(2)s). TbSP1, the sPLA(2) primarily addressed in this study, is up-regulated by nutrient deprivation and is preferentially expressed in the symbiotic stage of the ectomycorrhizal fungus Tuber borchii. A peculiar feature of this phospholipase and of its ortholog from the black truffle Tuber melanosporum is the presence of a 54-amino acid sequence of unknown functional significance, interposed between the signal peptide and the start of the conserved catalytic core of the enzyme. X-ray diffraction analysis of a recombinant TbSP1 form corresponding to the secreted protein previously identified in T. borchii mycelia revealed a structure comprising the five α-helices that form the phospholipase catalytic module but lacking the N-terminal 54 amino acids. This finding led to a series of functional studies that showed that TbSP1, as well as its T. melanosporum ortholog, is a self-processing pro-phospholipase A(2), whose phospholipase activity increases up to 80-fold following autoproteolytic removal of the N-terminal peptide. Proteolytic cleavage occurs within a serine-rich, intrinsically flexible region of TbSP1, does not involve the phospholipase active site, and proceeds via an intermolecular mechanism. Autoproteolytic activation, which also takes place at the surface of nutrient-starved, sPLA(2) overexpressing hyphae, may strengthen and further control the effects of phospholipase up-regulation in response to nutrient deprivation, also in the context of symbiosis establishment and mycorrhiza formation.
authors.affiliation: Laboratory of Functional Genomics and Protein Engineering, Biochemistry and Molecular Biology Unit, Department of Biosciences, University of Parma, Parco Area delle Scienze 23/A, I-43124 Parma, Italy.
authors.forename: Davide
authors.initials: D
authors.lastname: Cavazzini
authors.forename: Francesca
authors.initials: F
authors.lastname: Meschi
authors.forename: Romina
authors.initials: R
authors.lastname: Corsini
authors.forename: Angelo
authors.initials: A
authors.lastname: Bolchi
authors.forename: Gian Luigi
authors.initials: GL
authors.lastname: Rossi
authors.forename: Oliver
authors.initials: O
authors.lastname: Einsle
authors.forename: Simone
authors.initials: S
authors.lastname: Ottonello
mesh_terms: D000595:Amino Acid Sequence; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004789:Enzyme Activation; D004926:Escherichia coli / Q000235:genetics; D005656:Fungal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D025282:Mycelium / Q000201:enzymology* / Q000235:genetics; D038821:Mycorrhizae / Q000201:enzymology* / Q000235:genetics; D054467:Phospholipases A2 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D010944:Plants / Q000382:microbiology; D011499:Protein Processing, Post-Translational; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013559:Symbiosis / Q000502:physiology
chemical_list: D005656:Fungal Proteins; D011994:Recombinant Proteins; D054467:Phospholipases A2