Biology subjects

Tycko, R.

Publications and source records attributed to Tycko, R..

5 recordsLinked to original sources

bioRxiv2026

Polymorphic structures of rapidly twisting 40-residue amyloid-β fibrils

Fibrils formed by 40- and 42-residue amyloid-{beta} peptides (A{beta}40 and A{beta}42) are polymorphic, containing molecular structures that vary with growth conditions in ways that are not fully understood. Here we use cryogenic electron microscopy to characterize the structure of rapidly twisting A{beta}40 fibrils, for which the distance between apparent width minima in electron microscope images ("cross-over distances") is approximately 25 nm. From samples grown under a single set of growth conditions, we obtain high-resolution structures for three different rapidly twisting polymorphs. Although their cross-over distances are similar, the three rapidly twisting polymorphs differ in twist handedness, symmetry, molecular conformations, and intermolecular contacts. Two of the rapidly twisting polymorphs resemble slowly twisting A{beta}40 polymorphs that have been described previously, including polymorphs extracted from brain tissue of Alzheimers disease patients or created by seeded growth from amyloid in brain tissue, but with shorter conformationally ordered segments and other specific conformational differences. These results contribute to our understanding of amyloid polymorphism, connections between morphology and molecular structure, and relationships between brain-derived and in vitro-grown fibrils.

biophysics↗

bioRxiv2025

Effects of Nanopore Confinement on the Conformational, Dynamical, and Self-Assembly Properties of an FG-Repeat Peptide

The central channels of nuclear pore complexes (NPCs) in eukaryotic cells are filled with protein chains whose sequences contain characteristic phenylalanine-glycine motifs. Properties of these nanopore-confined FG-repeat sequences are of central importance to NPC function. Here we demonstrate an approach to nuclear magnetic resonance (NMR) studies of FG-repeat sequences (or other polypeptides) that are tethered within pores with diameters similar to those of NPC channels. By attaching alkyl phosphonate groups to the N-terminus of a 30-residue peptide that contains four FG repeats, called FG30, we tether FG30 chains to walls of 20-nm-diameter pores in anodic aluminum oxide (AAO) wafers through phosphonate-surface bonds. Quantitative 13C and 31P NMR measurements indicate 90 mM peptide concentrations (300 mg/ml) within the pores. NMR spectra and spin relaxation measurements show that FG30 chains are dynamically disordered and random-coil-like in buffer-filled pores over a broad temperature range. In contrast, FG30 aggregates in free solution at concentrations above 2 mM, forming structurally ordered fibrils according to electron microscopy and NMR measurements. These results demonstrate the utility of AAO as a scaffold for studies of polypeptides in nanopore-confined environments and show that tethering to nanopore walls can dramatically alter the self-assembly properties of an FG-repeat sequence. TOC Graphic O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=141 SRC="FIGDIR/small/675621v2_ufig1.gif" ALT="Figure 1"> View larger version (92K): org.highwire.dtl.DTLVardef@7e0287org.highwire.dtl.DTLVardef@d81553org.highwire.dtl.DTLVardef@601639org.highwire.dtl.DTLVardef@52fc7a_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2024

Conformations of a Low-Complexity Protein in Homogeneous and Phase-Separated Frozen Solutions

Solutions of the intrinsically disordered, low-complexity domain of the FUS protein (FUS-LC) undergo liquid-liquid phase separation (LLPS) below temperatures TLLPS in the 20-40{degrees} C range. To investigate whether local conformational distributions are detectably different in the homogeneous and phase-separated states of FUS-LC, we performed solid state nuclear magnetic resonance (ssNMR) measurements on solutions that were frozen on sub-millisecond time scales after equilibration at temperatures well above (50{degrees} C) or well below (4{degrees} C) TLLPS. Measurements were performed at 25 K with signal enhancements from dynamic nuclear polarization. Crosspeak patterns in two-dimensional (2D) ssNMR spectra of rapidly frozen solutions in which FUS-LC was uniformly 15N,13C-labeled were found to be nearly identical for the two states. Similar results were obtained for solutions in which FUS-LC was labeled only at Thr, Tyr, and Gly residues, as well as solutions of a FUS construct in which five specific residues were labeled by ligation of synthetic and recombinant fragments. These experiments show that local conformational distributions are nearly the same in the homogeneous and phase-separated solutions, despite the much greater protein concentrations and more abundant intermolecular interactions within phase-separated, protein-rich "droplets". Comparison of the experimental results with simulations of the sensitivity of 2D crosspeak patterns to an enhanced population of {beta}-strand-like conformations suggests that changes in conformational distributions are no larger than 5-10%. Statement of SignificanceLiquid-liquid phase separation (LLPS) in solutions of proteins with intrinsically disordered domains has attracted recent attention because of its relevance to multiple biological processes and its inherent interest from the standpoint of protein biophysics. The high protein concentrations and abundant intermolecular interactions within protein-rich, phase-separated "droplets" suggests that conformational distributions of intrinsically disordered proteins may differ in homogeneous and phase-separated solutions. To investigate whether detectable differences exist, we performed experiments on the low-complexity domain of the FUS protein (FUS-LC) in which FUS-LC solutions were first equilibrated at temperatures well above or well below their LLPS transition temperatures, then rapidly frozen and examined at very low temperatures by solid state nuclear magnetic resonance (ssNMR) spectroscopy. The ssNMR data for homogeneous and phase-separated frozen solutions of FUS-LC were found to be nearly identical, showing that LLPS is not accompanied by substantial changes in the local conformational distributions of this intrinsically disordered protein.

biophysics↗

bioRxiv2020

Transiently structured head domains control intermediate filament assembly

Low complexity (LC) head domains 92 and 108 residues in length are, respectfully, required for assembly of neurofilament light (NFL) and desmin intermediate filaments (IFs). As studied in isolation, these IF head domains interconvert between states of conformational disorder and labile, {beta}-strand-enriched polymers. Solid state nuclear magnetic resonance (ss-NMR) spectroscopic studies of NFL and desmin head domain polymers reveal spectral patterns consistent with structural order. A combination of intein chemistry and segmental isotope labeling allowed preparation of fully assembled NFL and desmin IFs that could also be studied by ss-NMR. Assembled IFs revealed spectra overlapping with those observed for {beta}-strand-enriched polymers formed from the isolated NFL and desmin head domains. Phosphorylation and disease causing mutations reciprocally alter NFL and desmin head domain self-association, yet commonly impede IF assembly. These observations show how facultative structural assembly of LC domains via labile, {beta}-strand-enriched self-interactions may broadly influence cell morphology.

biochemistry↗

bioRxiv2020

Molecular structure of a prevalent amyloid-β fibril polymorph from Alzheimer's disease brain tissue

Amyloid-{beta} (A{beta}) fibrils exhibit self-propagating, molecular-level polymorphisms that may underlie variations in clinical and pathological characteristics of Alzheimers disease. We report the molecular structure of a specific brain-derived polymorph that has been identified as the most prevalent polymorph of 40-residue A{beta} fibrils in cortical tissue of Alzheimers disease patients. This structure, developed from cryo-electron microscopy and supported by solid state NMR data, differs qualitatively from all previously described A{beta} fibril structures, both in its molecular conformation and its organization of cross-{beta} subunits. Knowledge of this brain-derived fibril structure may contribute to the development of structure-specific amyloid imaging agents and aggregation inhibitors with greater diagnostic and therapeutic utility.

biophysics↗