Ales Medek

Solution structure of the antiapoptotic protein bcl-2

The structures of two isoforms of Bcl-2 that differ by two amino acids have been determined by NMR spectroscopy. Because wild-type Bcl-2 behaved poorly in solution, the structures were determined by using Bcl-2/Bcl-xL chimeras in which part of the putative unstructured loop of Bcl-2 was replaced with a shortened loop from Bcl-xL. These chimeric proteins have a low pI compared with the wild-type protein and are soluble. The structures of the two Bcl-2 isoforms consist of 6 α-helices with a hydrophobic groove on the surface similar to that observed for the homologous protein, Bcl-xL. Comparison of the Bcl-2 structures to that of Bcl-xL shows that although the overall fold is the same, there are differences in the structural topology and electrostatic potential of the binding groove. Although the structures of the two isoforms of Bcl-2 are virtually identical, differences were observed in the ability of the proteins to bind to a 25-residue peptide from the proapoptotic Bad protein and a 16-residue peptide from the proapoptotic Bak protein. These results suggest that there are subtle differences in the hydrophobic binding groove in Bcl-2 that may translate into differences in antiapoptotic activity for the two isoforms.

Multiple - quantum magic - angle spinning NMR: a new technique for probing quadrupolar nuclei in solids

We have recently described a new technique capable of recording high resolution NMR spectra of half - integer quadrupolar nuclei in solid samples, based on the combined use of magic - angle - spinning (MAS) and multiple - quantum (MQ) spectroscopy1. This review summarizes the basic theoretical aspects underlying this high resolution MQMAS NMR experiment, emphasizing as well practical aspects involved in the optimization of its signal - to - noise. We also describe the features of MQMAS spectral lineshapes, and exemplify these with a number of applications on various quadrupolar nuclei. Also discussed is the occurrence of unusual spinning sideband patterns along the multiple - quantum domain; additional references to ongoing progress in the area that has appeared in the recent literature are also presented.

Multi‐rank nuclear magnetic resonance studies of half‐integer quadrupolar nuclei in solids by three‐dimensional dynamic‐angle correlation spectroscopy

The present work introduces a new three‐dimensional nuclear magnetic resonance (3D NMR) experiment for the analysis of half‐integer quadrupolar nuclei in solids. The method is based on the multi‐rank expansion of the high‐field NMR Hamiltonian governing the central transition of these spins in terms of irreducible spherical tensor elements. This approach leads to a temporal spin evolution given by an isotropic term characteristic of each chemical site, as well as by second‐ and fourth‐rank anisotropies depending on the principal values and relative orientations of the shielding and quadrupolar interactions. A method for extracting the 3D spectral distribution correlating these three frequency components is presented, based on the acquisition of dynamic‐angle spinning NMR signals collected as a function of different initial and final spinning axes. Computational and instrumental details involved in the acquisition of these 3D dynamic‐angle correlation spectroscopy (DACSY) data are discussed, and applicatio...