Spectroscopy

Looking at fast kinetic events by NMR

Although NMR spectroscopy is a fantastic technology for obtaining detailed information about proteins at the atomic level, it has been limited to studying kinetic processes on the order of minutes to hours. Schanda et al. now introduce SOFAST NMR spectroscopy, which reduces the time resolution to a few seconds. They used the SOFAST method to observe folding of α-lactalbumin and unfolding of ubiquitin.

Schanda, P. et al. Proc. Natl. Acad. Sci. USA 104, 11257–11262 (2007).

Stem cells

Large-scale human stem cell characterization

As a service to the community, the International Stem Cell Initiative has systematically characterized 59 independently derived human embryonic stem cell lines from 17 different laboratories. Remarkably, in testing the expression of 17 marker cell-surface antigens and 93 genes, they found common expression patterns in spite of the differences in genetic backgrounds and different protocols used.

The International Stem Cell Initiative, Nat. Biotechnol. 25, 803–816 (2007).

Imaging and visualization

Triplex molecular beacons

Molecular beacons are useful probes for analyzing nucleic acids. In their free state they form a quenched stem-loop structure, but upon binding a target sequence the stem-loop opens, restoring fluorescence. Grossman et al. describe the design of 'triplex' molecular beacons, which bind an additional stem-forming oligonucleotide sequence in their free state. Their modular assembly allows the introduction of other functionalities, such as an additional quencher.

Grossman, T.N. et al. Angew. Chem. Int. Ed. 46, 5223–5225 (2007).

Biophysics

Making porous vesicles

The encapsulation of biomolecules inside lipid bilayer vesicles offers a way to observe molecular interactions for extended periods. Expanding the capabilities of the technique, Cisse et al. describe methods for introducing pores into vesicles, allowing exchange of buffer and chemical conditions in a controlled manner while keeping the local protein concentration constant. The system shows promise for use in single-molecule experiments.

Cisse, I. et al. Proc. Natl. Acad. Sci. USA; published online 11 June 2007.

Chemical biology

Testing peptide permeability

Tools for modulating protein activity, cyclic peptides are more proteolytically resistant than their linear counterparts, and their constrained conformation may provide more favorable binding characteristics and potentially increase cell-permeability. Kwon and Kodadek used a reporter gene assay to quantitatively compare cell permeability, and found that cyclic peptides are not generally more permeable than linear peptides.

Kwon, Y.U. & Kodadek, T. Chem. Biol. 14, 671–677 (2007).