Biomedical subjects

J J Balbach

Publications and source records attributed to J J Balbach.

3 recordsLinked to original sources

PubMed2000

Multiple quantum solid-state NMR indicates a parallel, not antiparallel, organization of beta-sheets in Alzheimer's beta-amyloid fibrils.

Senile plaques associated with Alzheimer's disease contain deposits of fibrils formed by 39- to 43-residue beta-amyloid peptides with possible neurotoxic effects. X-ray diffraction measurements on oriented fibril bundles have indicated an extended beta-sheet structure for Alzheimer's beta-amyloid fibrils and other amyloid fibrils, but the supramolecular organization of the beta-sheets and other structural details are not well established because of the intrinsically noncrystalline, insoluble nature of amyloid fibrils. Here we report solid-state NMR measurements, using a multiple quantum (MQ) (13)C NMR technique, that probe the beta-sheet organization in fibrils formed by the full-length, 40-residue beta-amyloid peptide (Abeta(1-40)). Although an antiparallel beta-sheet organization often is assumed and is invoked in recent structural models for full-length beta-amyloid fibrils, the MQNMR data indicate an in-register, parallel organization. This work provides site-specific, atomic-level structural constraints on full-length beta-amyloid fibrils and applies MQNMR to a significant problem in structural biology.

Alanine↗

PubMed2000

Amyloid fibril formation by A beta 16-22, a seven-residue fragment of the Alzheimer's beta-amyloid peptide, and structural characterization by solid state NMR.

The seven-residue peptide N-acetyl-Lys-Leu-Val-Phe-Phe-Ala-Glu-NH(2), called A beta(16-22) and representing residues 16-22 of the full-length beta-amyloid peptide associated with Alzheimer's disease, is shown by electron microscopy to form highly ordered fibrils upon incubation of aqueous solutions. X-ray powder diffraction and optical birefringence measurements confirm that these are amyloid fibrils. The peptide conformation and supramolecular organization in A beta(16-22) fibrils are investigated by solid state (13)C NMR measurements. Two-dimensional magic-angle spinning (2D MAS) exchange and constant-time double-quantum-filtered dipolar recoupling (CTDQFD) measurements indicate a beta-strand conformation of the peptide backbone at the central phenylalanine. One-dimensional and two-dimensional spectra of selectively and uniformly labeled samples exhibit (13)C NMR line widths of <2 ppm, demonstrating that the peptide, including amino acid side chains, has a well-ordered conformation in the fibrils. Two-dimensional (13)C-(13)C chemical shift correlation spectroscopy permits a nearly complete assignment of backbone and side chain (13)C NMR signals and indicates that the beta-strand conformation extends across the entire hydrophobic segment from Leu17 through Ala21. (13)C multiple-quantum (MQ) NMR and (13)C/(15)N rotational echo double-resonance (REDOR) measurements indicate an antiparallel organization of beta-sheets in the A beta(16-22) fibrils. These results suggest that the degree of structural order at the molecular level in amyloid fibrils can approach that in peptide or protein crystals, suggest how the supramolecular organization of beta-sheets in amyloid fibrils can be dependent on the peptide sequence, and illustrate the utility of solid state NMR measurements as probes of the molecular structure of amyloid fibrils. A beta(16-22) is among the shortest fibril-forming fragments of full-length beta-amyloid reported to date, and hence serves as a useful model system for physical studies of amyloid fibril formation.

Amyloid beta-Peptides↗

PubMed2000

Probing hydrogen bonds in the antibody-bound HIV-1 gp120 V3 loop by solid state NMR REDOR measurements.

We describe solid state NMR measurements on frozen solutions of the complex of the 24-residue HIV-1 gp120 V3 loop peptide RP135 with the Fab fragment of the anti-gp120 antibody 0.5beta, using rotational echo double resonance (REDOR). In order to probe possible hydrogen bonding between arginine side chains and glycine backbone carbonyls in the region of the conserved Gly-Pro-Gly-Arg (GPGR) motif of the V3 loop, RP135 samples were prepared with 15N labels at the eta nitrogen positions of arginine side chains and 13C labels at glycine carbonyl positions and 13C-detected 13C-15N REDOR measurements were performed on peptide/antibody complexes of these labeled samples. Such hydrogen bonding was previously observed in a crystal structure of the V3 loop peptide/antibody complex RP142/59.1 [Ghiara et al. (1994) Science, 264, 82-85], but is shown by the REDOR measurements to be absent in the RP135/0.5beta complex. These results confirm the antibody-dependent conformational differences in the GPGR motif suggested by previously reported solid state NMR measurements of phi and psi backbone dihedral angles in the RP135/0.53 complex. In addition, we describe REDOR measurements on the helical synthetic peptide MB(i+4)EK in frozen solution that establish our ability to detect 13C-15N dipole-dipole couplings in the distance range appropriate to these hydrogen bonding studies. We also report the results of molecular modeling calculations on the central portion RP135, using a combination of the solid state NMR restraints of Weliky et al. [Nat. Struct. Biol., 6, 141-145, 1999] and the liquid state NMR restraints of Tugarinov et al. (Nat. Struct. Biol., 6, 331-335, 1999]. The dynamics calculations demonstrate the mutual compatibility of the two sets of experimental structural restraints and reduce ambiguities in the solid state NMR restraints that result from symmetry and signal-to-noise considerations.

Antigen-Antibody Complex↗