F GPI and sugars. Histological analysis of brains from several of the infected transgenic mice showed a characteristic PrP accumulation pattern, as previously described [15,16], with hyaline deposits arranged radially around blood vessels. Those deposits were strongly immunoreactive to PrP monoclonal antibody 6H4. Deposits were also located 
submeningeally, subventricularly and scattered in the neuropil (Figure 1B). In order to verify that the GPI- PrPSc was infective, a group of ten Pleuromutilin price wild-type (C57BL/6) mice were inoculated with brain homogenate prepared from one of the infected transgenic mice. All ten 15900046 of these wild-type mice became ill with clinical signs characteristic of the RML strain of murineadapted scrapie and were humanely euthanized. The incubation period of the disease was 154615 days post-inoculation (Figure 1C).Kinetics of PK Digestion in GPI-anchorless PrPScWe performed a PK-digestion time course to determine the relationship of these peptides to one another. A time-dependent reduction in intensity of all purchase Tubastatin-A PK-resistant bands was observed (Figure 4). The intensities of the 17, 14.6, 13, 12, and 6.7 kDa bands decreased steadily over time. By 240 minutes the intensities of the 17 and 10.2 kDa bands are nearly equal and by 360 minutes the intensity of the 17, 10.2 and 8 kDa bands are similar. These results are consistent with a progressive digestion of GPI- PrPSc from the N-terminus. This further suggests that different PKresistant fragments are not from different sub-populations of GPIPrPSc, instead they are derived from a larger common GPI- PrPSc peptide.Identification of PK Cleavage Sites in GPI-anchorless PrPSc by Mass Spectrometric DetectionWe isolated PK-resistant PrPSc fragments from infected GPI2 brains. Purity of this material was assessed by SDS-PAGE followed by Coomassie staining (Figure S2). Using a high resolution Tricine/SDS-PAGE system [17], we compared the distribution of these fragments with that of fragments present in PK-treated unpurified GPI2 infected brain homogenate, and found them to be similar, which demonstrates that our purification process isolates all of the PK-resistant fragments (Figure S3). GPI2 PrPSc, unlike wild-type PrPSc, permits the use of MS to accurately identifyPK Cleavage Analysis After Partial Unfolding of GPIanchorless PrPScThe above observations were confirmed when the GPI2 PrPSc was partially unfolded with increasing concentrations of 
guanidine prior to PK cleavage, following the procedure of Kocisko et al. [18]. These authors have shown that partial unfolding of PrPSc with up to 2.5? M guanidine is reversible upon dialysis. GPIStructural Organization of Mammalian PrionsFigure 1. Characterization of GPI- PrPSc. A. Western blot of brain homogenate from scrapie-infected GPI2 tg mouse before and after digestion with PK (25 mg/ml); WB probed with SAF83 antibody. B. Histopathological and immunohistochemical analyses of scrapie-infected GPI2 tg mouse brain. (a) Haematoxylin-eosin staining of the hippocampal formation. (b) IHC staining (antibody 6H4) of the hippocampal formation. C. Kaplan-Meier survival curves of wild-type mice (C57BL/6) inoculated with 2 of brain homogenate from scrapie-infected GPI2 PrPSc (green line) and a negative control inoculated with PBS (red line). doi:10.1371/journal.pone.0050111.gPrPSc became more susceptible to proteolytic digestion in a guanidine-concentration dependent manner. At concentrations above 1 M, the 10.2 and, to a lesser extent, 12 and 8 kDa bands (.F GPI and sugars. Histological analysis of brains from several of the infected transgenic mice showed a characteristic PrP accumulation pattern, as previously described [15,16], with hyaline deposits arranged radially around blood vessels. Those deposits were strongly immunoreactive to PrP monoclonal antibody 6H4. Deposits were also located submeningeally, subventricularly and scattered in the neuropil (Figure 1B). In order to verify that the GPI- PrPSc was infective, a group of ten wild-type (C57BL/6) mice were inoculated with brain homogenate prepared from one of the infected transgenic mice. All ten 15900046 of these wild-type mice became ill with clinical signs characteristic of the RML strain of murineadapted scrapie and were humanely euthanized. The incubation period of the disease was 154615 days post-inoculation (Figure 1C).Kinetics of PK Digestion in GPI-anchorless PrPScWe performed a PK-digestion time course to determine the relationship of these peptides to one another. A time-dependent reduction in intensity of all PK-resistant bands was observed (Figure 4). The intensities of the 17, 14.6, 13, 12, and 6.7 kDa bands decreased steadily over time. By 240 minutes the intensities of the 17 and 10.2 kDa bands are nearly equal and by 360 minutes the intensity of the 17, 10.2 and 8 kDa bands are similar. These results are consistent with a progressive digestion of GPI- PrPSc from the N-terminus. This further suggests that different PKresistant fragments are not from different sub-populations of GPIPrPSc, instead they are derived from a larger common GPI- PrPSc peptide.Identification of PK Cleavage Sites in GPI-anchorless PrPSc by Mass Spectrometric DetectionWe isolated PK-resistant PrPSc fragments from infected GPI2 brains. Purity of this material was assessed by SDS-PAGE followed by Coomassie staining (Figure S2). Using a high resolution Tricine/SDS-PAGE system [17], we compared the distribution of these fragments with that of fragments present in PK-treated unpurified GPI2 infected brain homogenate, and found them to be similar, which demonstrates that our purification process isolates all of the PK-resistant fragments (Figure S3). GPI2 PrPSc, unlike wild-type PrPSc, permits the use of MS to accurately identifyPK Cleavage Analysis After Partial Unfolding of GPIanchorless PrPScThe above observations were confirmed when the GPI2 PrPSc was partially unfolded with increasing concentrations of guanidine prior to PK cleavage, following the procedure of Kocisko et al. [18]. These authors have shown that partial unfolding of PrPSc with up to 2.5? M guanidine is reversible upon dialysis. GPIStructural Organization of Mammalian PrionsFigure 1. Characterization of GPI- PrPSc. A. Western blot of brain homogenate from scrapie-infected GPI2 tg mouse before and after digestion with PK (25 mg/ml); WB probed with SAF83 antibody. B. Histopathological and immunohistochemical analyses of scrapie-infected GPI2 tg mouse brain. (a) Haematoxylin-eosin staining of the hippocampal formation. (b) IHC staining (antibody 6H4) of the hippocampal formation. C. Kaplan-Meier survival curves of wild-type mice (C57BL/6) inoculated with 2 of brain homogenate from scrapie-infected GPI2 PrPSc (green line) and a negative control inoculated with PBS (red line). doi:10.1371/journal.pone.0050111.gPrPSc became more susceptible to proteolytic digestion in a guanidine-concentration dependent manner. At concentrations above 1 M, the 10.2 and, to a lesser extent, 12 and 8 kDa bands (.
