Session WOB. There are 5 abstracts in this session.

Session: BIOMOLECULAR 3 - DISORDER IN PROTEINS, time: 08:30 - 8:55 am

13C Direct-Detect NMR of Intrinsically Disordered Proteins

Scott Showalter
The Pennsylvania State University, University Park,

Structure-function relationships involving Intrinsically Disordered Proteins (IDPs) are under-studied because their extreme sequence bias presents a technical barrier to NMR spectroscopy, while their flexibility precludes crystallization. We are among a group of laboratories that have shown 13C direct-detect NMR is uniquely well-suited to overcoming this barrier. Our progress will be illustrated through recent work on the RNA Polymerase II C-terminal Domain (CTD), which undergoes sequence-specific proline trans-to-cis isomerization upon serine phosphorylation, ultimately read out by downstream enzymes. These and other results depend on 13C direct-detect NMR, which efficiently generates comprehensive chemical shift sets for disordered systems, along with structural and dynamics constraints that contribute the mechanistic information needed to put the structural biology of IDPs into a biochemically useful perspective.

Session: BIOMOLECULAR 3 - DISORDER IN PROTEINS, time: 08:55 - 9:20 am

Transient Biomolecular Structures from DNP-Enhanced, Millisecond Time-Resolved Solid State NMR

Robert Tycko; Jaekyun Jeon; Wai-Ming Yau; Kent Thurber
National Institutes of Health, Bethesda, MD

An approach will be described for characterizing transient intermediates in biomolecular structural conversion processes that occur on millisecond time scales, using a combination of rapid mixing, rapid freeze-quenching, solid state NMR, and low-temperature dynamic nuclear polarization.  Experimental results will be presented for the process by which the 26-residue peptide melittin converts from an unstructured monomeric state at pH 3 to a helical, tetrameric state after a rapid jump to pH 7.  The latest results from ongoing experiments on other systems will also be presented.. 

Session: BIOMOLECULAR 3 - DISORDER IN PROTEINS, time: 09:20 - 9:35 am

Functional interactions between a Kir Channel and the lipid bilayer

Benjamin Wylie; Collin Borcik; Reza Amani; Nazmul Khan; Derek Versteeg; Maryam Yekefallah; Evan val Aalst
Texas Tech University, Lubbock, TX

KirBac1.1 is a tetrameric inward-rectifier K+ (Kir) channel.  Its structure includes a selectivity filter which allows K+ ions  to pass through the bilayer,  eight transmembrane helices, and a cytoplasmic “Kir domain”.  The Kir domain tethers to anionic lipids, gating the channel. Using solid-state NMR, we identified the activating anionic lipid binding pocket within KirBac1.1 and determined the changes in dynamic structure associated with channel gating.  We discovered two states of the channel under gating conditions.  One state is activated and conductive and the second state appears to be shallowly inactivated. Further, using 13C-labeled biological lipids, we show that KirBac1.1 lowers the gel-liquid crystalline phase transition of the surrounding bilayer and increases the liquid-ordered (Lo)/liquid-disordered (Ld) phase separation of these membranes.

Session: BIOMOLECULAR 3 - DISORDER IN PROTEINS, time: 09:35 - 9:50 am

Cross Seeding between Fibrillar Beta-Amyloid Variants: Accelerated Aggregation, Propagated Molecular Polymorphisms and Elevated Cellular Toxicities

Zhi-Wen Hu1; Letticia Cruceta1; Dan Fai Au2; Liliya Vugmeyster2; Yan Sun1; Wei Qiang1
1Binghamton University, Binghamton, New York; 2University of Colorado Denver, Denver, CO

Recent solid-state NMR works showed the potential correlation between molecular polymorphisms in 40-residue β-amyloid (Aβ40) fibrils and the clinic histories of AD patients, which, for the first time, unraveled the pathological significance of molecular-level structural variations in Aβ plaques. However, it remains unknown how the fibrillar structural variations might lead to pathological consequences. We show in this work, using a series of post-translational modified Aβ40 (PTM-Aβ40) variants, that the cross seeding between Aβ40 variants could serve as key events in AD pathology. The toxicity levels of wt-Aβ40 fibrils could be manipulated by the presence of other Aβ variants. And the propagation of molecular polymorphisms in fibrillar Aβ variants may be the underline mechanisms for the changes in cellular toxicities.

Session: BIOMOLECULAR 3 - DISORDER IN PROTEINS, time: 09:50 - 10:05 am

Dissecting the interactions of emerging nascent chains with the ribosome surface using NMR spectroscopy

Christopher Waudby; Anaïs Cassaignau; Charles Burridge; Tomasz Wlodarksi; Sammy Chan; Lisa Cabrita; John Christodoulou
University College London, London, United Kingdom

The folding of many proteins can begin during biosynthesis on the ribosome, and in some cases this may be modulated through interactions between the nascent chain and the ribosome surface. We have previously used solution-state NMR to characterise co-translational folding in translationally-arrested ribosome–nascent chain complexes. Here, we will describe the use of chemical shift covariance analysis and new sensitivity-optimised measurements of cross-correlated relaxation in amide and methyl spin systems to study dynamics in both folded and unfolded ribosome–nascent chain complexes. Using these methods we can quantify, with residue-specific resolution, interactions between nascent polypeptides and the associated ribosome surface, and so deduce the impact of such interactions on the free energy landscapes associated with the co-translational folding process.