Persistence of Methionine Side Chain Mobility at Low Temperatures in a Nine-Residue Low Complexity Peptide, as Probed by H Solid-State NMR.

Methionine side chains are flexible entities which play important roles in defining hydrophobic interfaces. We utilize deuterium static solid-state NMR to assess rotameric inter-conversions and other dynamic modes of the methionine in the context of a nine-residue random-coil peptide (RC9) with the low-complexity sequence GGKGMGFGL. The measurements in the temperature range of 313 to 161 K demonstrate that the rotameric interconversions in the hydrated solid powder state persist to temperatures below 200 K.

Modulation of aggregation and structural polymorphisms of β-amyloid fibrils in cellular environments by pyroglutamate-3 variant cross-seeding.

Amyloidogenic deposition of β-amyloid (Aβ) peptides in human brain involves not only the wild-type Aβ (wt-Aβ) sequences, but also posttranslationally modified Aβ (PTM-Aβ) variants. Recent studies hypothesizes that the PTM-Aβ variants may trigger the deposition of wt-Aβ, which underlies the pathology of Sporadic Alzheimer's disease. Among PTM-Aβ variants, the pyroglutamate-3-Aβ (E3-Aβ) has attracted much attention because of their significant abundances and broad distributions in senile plaques and dispersible and soluble oligomers.

Deuteron off-resonance rotating frame relaxation for the characterization of slow motions in rotating and static solid-state proteins.

We demonstrate the feasibility of deuterium solid-state NMR off-resonance rotating frame relaxation measurements for studies of slow motions in biomolecular solids. The pulse sequence, which includes adiabatic pulses for magnetization alignment, is illustrated for static and magic-angle spinning conditions away from rotary resonances. We apply the measurements for three systems with selective deuterium labels at methyl groups: a) a model compound, Fluorenylmethyloxycarbonyl methionine-D amino acid, for which the principles of the measurements and corresponding motional modeling based on rotameric interconversions are demonstrated; b) amyloid-β fibrils labeled at a single alanine methyl group located in the disordered N-terminal domain.

Effect of Cross-Seeding of Wild-Type Amyloid-β Peptides with Post-translationally Modified Fibrils on Internal Dynamics of the Fibrils Using Deuterium Solid-State NMR.

Post-translationally modified (PTM) amyloid-β (Aβ) species can play an important role in modulating Alzheimer's disease pathology. These relatively less populated modifications can cross-seed the wild-type Aβ peptides to produce fibrils that retain many structural and functional features of the original PTM variants. We focus on studies of internal flexibility in the cross-seeded Aβ fibrils originating from seeding with two PTM variants with modifications in the disordered N-terminal domain: Δ3 truncation and S8-phosphorylation.

Nine-residue low-complexity disordered peptide as a model system, an NMR/CD study.

Disordered proteins and protein segments can be crucial for biological function. In this work we present a detailed biophysical characterization of the low-complexity nine-residue peptide with the sequence GGKGMGFGL. Based on proton solution NMR chemical shifts, circular dichroism measurements, as well as the analysis of concentration dependence of NMR linewidth, proton longitudinal relaxation times, hydrogen-deuterium exchange measurements, and 15N rotating frame NMR relaxation measurements, we conclude that the peptide is fully disordered and monomeric in solution.