Amino acid selective unlabeling for sequence specific resonance assignments in proteins

Sequence specific resonance assignment constitutes an important step towards high-resolution structure determination of proteins by NMR and is aided by selective identification and assignment of amino acid types. The traditional approach to selective labeling yields only the chemical shifts of the particular amino acid being selected and does not help in establishing a link between adjacent residues along the polypeptide chain, which is important for sequential assignments. An alternative approach is the method of amino acid selective `unlabeling' or reverse labeling, which involves selective unlabeling of specific amino acid types against a uniformly C-13/N-15 labeled background. Based on this method, we present a novel approach for sequential assignments in proteins. The method involves a new NMR experiment named, {(CO)-C-12 (i) -N-15 (i+1)}-filtered HSQC, which aids in linking the H-1(N)/N-15 resonances of the selectively unlabeled residue, i, and its C-terminal neighbor, i + 1, in HN-detected double and triple resonance spectra. This leads to the assignment of a tri-peptide segment from the knowledge of the amino acid types of residues: i - 1, i and i + 1, thereby speeding up the sequential assignment process. The method has the advantage of being relatively inexpensive, applicable to H-2 labeled protein and can be coupled with cell-free synthesis and/or automated assignment approaches. A detailed survey involving unlabeling of different amino acid types individually or in pairs reveals that the proposed approach is also robust to misincorporation of N-14 at undesired sites. Taken together, this study represents the first application of selective unlabeling for sequence specific resonance assignments and opens up new avenues to using this methodology in protein structural studies

Membrane-embedded TSPO: an NMR view

Translocator Protein (18 kDa) (TSPO) is a mitochondrial transmembrane protein commonly used as a biomarker for neuroinflammation and is also a potential therapeutic target in neurodegenerative diseases. Despite intensive research efforts, the function of TSPO is still largely enigmatic. Deciphering TSPO structure in the native lipid environment is essential to gain insight into its cellular activities and to design improved diagnostic and therapeutic ligands. Here, we discuss the influence of lipid composition on the structure of mammalian TSPO embedded into lipid bilayers on the basis of solid-state NMR experiments. We further highlight that cholesterol can influence both the tertiary and quaternary TSPO structure and also influence TSPO localization in mitochondria-associated endoplasmic reticulum membranes

Transnational Governance as Contested Institution-Building: China, Merchants, and Contract Rules in the Cotton Trade

We are in an era of uncertainty over whose rules will govern global economic integration. With the growing market share of Chinese firms and the power of the Chinese state it is unclear if Western firms will continue to dominate transnational governance. Exploring these dynamics through a study of contract rules in the global cotton trade, this article conceptualizes commodity chain governance as a contested process of institution-building. To this end, the global commodity chain/global value chain (GCC/GVC) framework must be revised to better account for the broader institutional context of commodity chain governance, institutional variation across space, and strategic action in the construction of legitimate governance arrangements. I provide a more dynamic model of GCC governance that stresses how strategic action, existing institutions, and dominant discourses intersect as firms and states compete for institutional power within a commodity chain. This advances our understandings of how commodity chain governance emerges and changes over time

New methods for NMR spectral analysis

A set of novel methods for signal enhancement and artifact suppression in multidimensional NMR spectra have been developed. These methods, independent of the experiment type, aim at improvising resonance assignments, accurate measurement of NMR parameters and automated peak picking in spectra acquired with low sensitivity or containing artifacts