Polyglutamine Dances the Conformational Cha-Cha-Cha

While polyglutamine repeats appear in dozens of human proteins, high-resolution structural analysis of these repeats in their native context has eluded researchers. Kim et al. now describe multiple crystal structures and demonstrate that polyglutamine in huntingtin dances through multiple conformations

X-ray Structures of the Signal Recognition Particle Receptor Reveal Targeting Cycle Intermediates

The signal recognition particle (SRP) and its conjugate receptor (SR) mediate cotranslational targeting of a subclass of proteins destined for secretion to the endoplasmic reticulum membrane in eukaryotes or to the plasma membrane in prokaryotes. Conserved active site residues in the GTPase domains of both SRP and SR mediate discrete conformational changes during formation and dissociation of the SRP·SR complex. Here, we describe structures of the prokaryotic SR, FtsY, as an apo protein and in two different complexes with a non-hydrolysable GTP analog (GMPPNP). These structures reveal intermediate conformations of FtsY containing GMPPNP and explain how the conserved active site residues position the nucleotide into a non-catalytic conformation. The basis for the lower specificity of binding of nucleotide in FtsY prior to heterodimerization with the SRP conjugate Ffh is also shown. We propose that these structural changes represent discrete conformational states assumed by FtsY during targeting complex formation and dissociation

X-ray structures of the signal recognition particle receptor reveal targeting cycle intermediates.

The signal recognition particle (SRP) and its conjugate receptor (SR) mediate cotranslational targeting of a subclass of proteins destined for secretion to the endoplasmic reticulum membrane in eukaryotes or to the plasma membrane in prokaryotes. Conserved active site residues in the GTPase domains of both SRP and SR mediate discrete conformational changes during formation and dissociation of the SRP.SR complex. Here, we describe structures of the prokaryotic SR, FtsY, as an apo protein and in two different complexes with a non-hydrolysable GTP analog (GMPPNP). These structures reveal intermediate conformations of FtsY containing GMPPNP and explain how the conserved active site residues position the nucleotide into a non-catalytic conformation. The basis for the lower specificity of binding of nucleotide in FtsY prior to heterodimerization with the SRP conjugate Ffh is also shown. We propose that these structural changes represent discrete conformational states assumed by FtsY during targeting complex formation and dissociation

Amino-terminal domain stability mediates apolipoprotein E aggregation into neurotoxic fibrils

The three isoforms of apolipoprotein (apo) E are strongly associated with different risks for Alzheimer's disease: apoE4 > apoE3 > apoE2. Here, we show at physiological salt concentrations and pH that native tetramers of apoE form soluble aggregates in vitro that bind the amyloid dyes thioflavin T and Congo red. However, unlike classic amyloid fibrils, the aggregates adopt an irregular protofilament-like morphology and are seemingly highly alpha-helical. The aggregates formed at substantially different rates (apoE4 > apoE3 > apoE2) and were significantly more toxic to cultured neuronal cells than the tetramer. Since the three isoforms have large differences in conformational stability that can influence aggregation and amyloid pathways, we tested the effects of mutations that increased or decreased stability. Decreasing the conformational stability of the amino-terminal domain of apoE increased aggregation rates and vice versa. Our findings provide a new perspective for an isoform-specific pathogenic role for apoE aggregation in which differences in the conformational stability of the amino-terminal domain mediate neurodegeneration. (c) 2006 Elsevier Ltd. All rights reserved

N1 mediates domain shift between the N and G domains.

<p>(A) FtsY:GMPPNP, (B) FtsY:GDP, and (C) apo FtsY superimposed with FtsY:GMPPCP from the targeting complex with Ffh (transparent grey) (alignment on P-loop as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000607#pone-0000607-g005" target="_blank">Figure 5</a>). The N/G domain organization is similar for the apo, monomeric GMPPNP-bound form and complex form of FtsY, but differs in the GDP structure. Deletion of the N1 helix (cyan) in the GDP structure allows for this observed shift in the N-domain (blue) relative to the G-domain (green).</p

SRP-induced nucleotide specificity of FtsY.

<p>The specificity-determining hydrogen bonding interactions between GMPPNP and Asp258 are on average 0.6 Å more distant in the (A) monomeric nucleotide bound form of FtsY (F1) than for (D) FtsY in complex with Ffh. This additional spacing allows for the non-specific binding and hydrolysis of (B) ATP and (C) XTP in the monomeric form but not the complexed form of FtsY as observed in biochemical studies by Shan and Walter <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000607#pone.0000607-Shan3" target="_blank">[24]</a>. The ATP and XTP molecules were modeled based on the position of GMPPNP in the monomeric form of FtsY (F1).</p