title: Phthalocyanine tetrasulfonates bind to multiple sites on natively-folded prion protein.
abstract: The phthalocyanine tetrasulfonates (PcTS), a class of cyclic tetrapyrroles, bind to the mammalian prion protein, PrP. Remarkably, they can act as anti-scrapie agents to prevent the formation and spread of infectious, misfolded PrP. While the effects of phthalocyanines on the diseased state have been investigated, the interaction between PcTS and PrP has not yet been extensively characterized. Here we use multiple, complementary assays (surface plasmon resonance, isothermal titration calorimetry, fluorescence correlation spectroscopy, and tryptophan fluorescence quenching) to characterize the binding of PcTS to natively-folded hamster PrP(90-232), in order to determine binding constants, ligand stoichiometry, influence of buffer ionic strength, and the effects of chelated metal ions. We found that binding strength depends strongly on chelated metal ions, with Al(3+)-PcTS binding the weakest and free-base PcTS the strongest of the three types tested (Al(3+), Zn(2+), and free-base). Buffer ionic strength also affected the binding, with K(d) increasing along with salt concentration. The binding isotherms indicated the presence of at least two different binding sites with micromolar affinities and a total stoichiometry of ~4-5 PcTS molecules per PrP molecule.
authors.affiliation: Department of Physics, University of Alberta, Edmonton AB, Canada.
authors.forename: Derek R
authors.initials: DR
authors.lastname: Dee
authors.forename: Amar Nath
authors.initials: AN
authors.lastname: Gupta
authors.forename: Max
authors.initials: M
authors.lastname: Anikovskiy
authors.forename: Iveta
authors.initials: I
authors.lastname: Sosova
authors.forename: Elena
authors.initials: E
authors.lastname: Grandi
authors.forename: Laura
authors.initials: L
authors.lastname: Rivera
authors.forename: Abhilash
authors.initials: A
authors.lastname: Vincent
authors.forename: Angela M
authors.initials: AM
authors.lastname: Brigley
authors.forename: Nils O
authors.initials: NO
authors.lastname: Petersen
authors.forename: Michael T
authors.initials: MT
authors.lastname: Woodside
mesh_terms: D000535:Aluminum / Q000737:chemistry; D000818:Animals; D001665:Binding Sites; D002021:Buffers; D002151:Calorimetry; D056831:Coordination Complexes / Q000737:chemistry*; D006224:Cricetinae; D007211:Indoles / Q000737:chemistry*; D008647:Mesocricetus; D009994:Osmolar Concentration; D018621:PrPC Proteins / Q000737:chemistry*; D011485:Protein Binding; D013050:Spectrometry, Fluorescence; D020349:Surface Plasmon Resonance; D014364:Tryptophan / Q000737:chemistry; D015032:Zinc / Q000737:chemistry
chemical_list: D002021:Buffers; D056831:Coordination Complexes; D007211:Indoles; D018621:PrPC Proteins; C028418:tetrasulfophthalocyanine; D014364:Tryptophan; D000535:Aluminum; D015032:Zinc