Structural Polymorphism in Tau Filaments: An Implication for Neurodegenerative Diseases

Tau filaments are the pathological hallmark of >20 neurodegenerative diseases including Alzheimer's disease, Pick's disease, and progressive supranuclear palsy. In the adult human brain, six isoforms of tau are expressed that differ by presence or absence of the second of the four semiconserved repeats. As a consequence, half of the tau isoforms have three repeats (3R tau), whereas the other half has four repeats (4R tau). Site-directed spin labeling of recombinant tau in conjunction with electron paramagnetic resonance spectroscopy was used to obtain structural insights into tau filaments. The studies showed that the filaments of 4R tau and 3R tau share a highly ordered core structure in the third repeat with parallel, in-register arrangement of beta-strands. This structure in 3R and 4R is conserved regardless of whether full-length isoforms (htau40 and htau23) or truncated constructs (K18 and K19) are used. When mixed, 3R tau and 4R tau coassembled into heterogeneous filaments. Hence, these findings indicate that there are at least three compositionally distinct types of filaments: homogeneous 3R tau, homogeneous 4R tau, and heterogeneous 3R/4R tau. In vitro experiments show that the seeded filament growth, a prerequisite for tau spreading in tissue culture and brain, is crucially dependent on the isoform composition of individual seeds. Seeds of 3R tau and 3R/4R tau recruit both types of isoforms whereas seeds of 4R tau can recruit 4R tau, but not 3R tau, establishing an asymmetric barrier. Conformational templating of 4R tau onto 3R tau seeds eliminates this barrier, giving rise to a new type of tau filament. Conformational studies at the molecular level of tau filaments were done using Double electron-electron resonance spectroscopy, which allows the determination of distances between pairs of spin labels. These studies revealed structural differences between filaments of 3R tau and 4R tau. Furthermore, they indicated that 4R tau assumed the conformation of 3R tau when templated on 3R tau seeds. Our measurements have also provided insights into the heterogeneity of tau filament structure. Conformational differences due to variation in filament composition and seeding properties of tau filaments have shown that they are structurally polymorphic in nature. This structural polymorphism of tau filaments has widespread implications in understanding and treatment of neurodegenerative diseases.

Amino Acid Residues Implicated in the Interaction of Melanocortin Ligands and their Receptors: A Study of MC2R Selectivity

Author: Kristopher D. Veo Title: Amino acid residues implicated in the interaction of Melanocortin ligands and their receptors: A study of MC2R selectivity Advisor: Dr. Robert M. Dores Degree Date: August 2009 ABSTRACT Melanocortin receptor ligand selectivity has been a question not easily answered. The inability to functionally express melanocortin 2 receptor (MC2R) has inhibited the study of why MC2R is only stimulated by ACTH, a melanocortin hormone. With the recent discovery of the MC2R accessory protein (MRAP), creating a heterologous system is now feasible. Using a general cell line like CHO-K1 cells, which do not express endogenous MCRs, we were able to create a heterologous expression system and test the selectivity of MC2R using analog variants of ACTH(1-24). Our results indicate an amino acid requirement in the C-terminal portion of ACTH(1-24) for activation, which supports the 2-step method of activation hypothesized for MC2R. This site, the tetra basic cleavage site, when altered does not stimulate cAMP production and does not compete with ACTH(1-24) for binding. We also demonstrate the potential for a non-mammalian MC2R system in cloning full length Silurana tropicalis MC2R and completed localization studies with this system with MRAP using CHO-K1 cells.

Privy Private Eye: A Guidebook for Travelers Who Have to Go

This creative Capstone project, Privy Private Eye: A Guidebook for Travelers Who Have to Go, contains a nonfiction compendium of brief reviews of public restrooms in the Dallas, Texas area. To inform readers about facilities that are safe (and a few that should be avoided), Privy Private Eye contains reviews and ratings of restrooms in gas stations, restaurants, and retail centers. These appraisals will be featured in a full-length manuscript that may be published in the near future as a travel guide. Also contained herein, before the creative portion of the project itself, is a reflective paper describing the project, its creation, and its position within the context of published travel guides.