ABSTRACT
We agree with the author that a quantitative analysis of the predictive nature of the metrics used in graduate student admissions is a worthy pursuit and value the sincere intentions behind the UCSF Tetrad study. However, these types of analyses would benefit from the same rigorous approaches that we employ in our other research endeavors. As UCSF Tetrad graduates with diverse careers in academia, medicine, industry, and publishing, we hope that the definition of success in graduate school can be as thoughtfully and scientifically examined as the measurements used to select the next young people to follow in our footsteps.
Subject(s)
Education, Graduate , School Admission Criteria/trends , Students/statistics & numerical data , Female , Humans , MaleABSTRACT
On our initial discovery that prion protein (PrP)-derived peptides were capable of capturing the pathogenic prion protein (PrP(Sc)), we have been interested in how these peptides interact with PrP(Sc). After screening peptides from the entire human PrP sequence, we found two peptides (PrP(19-30) and PrP(100-111)) capable of binding full-length PrP(Sc) in plasma, a medium containing a complex mixture of other proteins including a vast excess of the normal prion protein (PrP(C)). The limit of detection for captured PrP(Sc) was calculated to be 8 amol from a approximately 10(5)-fold dilution of 10% (wt/vol) human variant Creutzfeldt-Jakob disease brain homogenate, with >3,800-fold binding specificity to PrP(Sc) over PrP(C). Through extensive analyses, we show that positively charged amino acids play an important, but not exclusive, role in the interaction between the peptides and PrP(Sc). Neither hydrophobic nor polar interactions appear to correlate with binding activity. The peptide-PrP(Sc) interaction was not sequence-specific, but amino acid composition affected binding. Binding occurs through a conformational domain that is only present in PrP(Sc), is species-independent, and is not affected by proteinase K digestion. These and other findings suggest a mechanism by which cationic domains of PrP(C) may play a role in the recruitment of PrP(C) to PrP(Sc).
Subject(s)
Peptide Fragments/chemical synthesis , PrPC Proteins/chemical synthesis , PrPSc Proteins/chemical synthesis , Antibodies/metabolism , Humans , Immunoglobulin G/metabolism , Microspheres , Peptide Fragments/blood , Peptide Fragments/immunology , PrPC Proteins/blood , PrPC Proteins/classification , PrPC Proteins/immunology , PrPSc Proteins/blood , PrPSc Proteins/classification , PrPSc Proteins/immunology , Prion Diseases/diagnosis , Prion Diseases/immunology , Protein BindingABSTRACT
Because the insolubility of the scrapie prion protein (PrP(Sc)) has frustrated structural studies by x-ray crystallography or NMR spectroscopy, we used electron crystallography to characterize the structure of two infectious variants of the prion protein. Isomorphous two-dimensional crystals of the N-terminally truncated PrP(Sc) (PrP 27-30) and a miniprion (PrP(Sc)106) were identified by negative stain electron microscopy. Image processing allowed the extraction of limited structural information to 7 A resolution. By comparing projection maps of PrP 27-30 and PrP(Sc)106, we visualized the 36-residue internal deletion of the miniprion and localized the N-linked sugars. The dimensions of the monomer and the locations of the deleted segment and sugars were used as constraints in the construction of models for PrP(Sc). Only models featuring parallel beta-helices as the key element could satisfy the constraints. These low-resolution projection maps and models have implications for understanding prion propagation and the pathogenesis of neurodegeneration.
