Imaging and visualization

Fluorescent reporter proteins without oxygen

Fluorescent proteins such as GFP are extremely useful, genetically encodable probes for biological imaging. All proteins derived from the GFP family, however, require molecular oxygen as a cofactor for chromophore fluorescence and therefore cannot be used in anaerobic systems. Drepper et al. now describe the engineering of blue-light flavin mononucleotide–based fluorescent proteins that do not require oxygen for formation of the chromophore. These proteins should find application for imaging in anaerobic microbes or hypoxic solid tumors.

Drepper, T et al. Nat. Biotechnol. 25, 443–445 (2007).

Gene transfer

Guiding Sleeping Beauty

Transposons are mobile genetic elements that integrate into the genome at random. Although the efficiency of their integration makes them suitable as gene delivery vectors, their unspecific insertion can be problematic when it disrupts genes or regulatory elements. Yant et al. now show that by fusing the Sleeping Beauty transposon to a DNA-binding domain, they can direct the integration to specific sequences in human cells.

Yant, S.R. et al. Nucleic Acids Res.; published online 7 March 2007.

Microarrays

Making protein arrays with AFM

Atomic force microscopy (AFM) is a useful technology for manipulating molecules on surfaces. Though it showed potential for the creation of protein arrays, this application was limited to very stable proteins, as it required relatively harsh conditions unfriendly to delicate proteins. Tinazli et al. now demonstrate the fabrication of 'rewritable' protein nanoarrays under physiological conditions using AFM-based nanolithography.

Tinazli, A. et al. Nat. Nanotechnol. 2, 220–225 (2007).

Biophysics

Tethering with bacteriophage

Khalil et al. describe the application of the M13 filamentous bacteriophage as a tether in single-molecule assays. Through genetic manipulation, reactive groups can be displayed on one end of the bacteriophage for tethering to a bead, while proteins of interest can be displayed on the phage surface for biophysical investigation. The authors describe a robust method for generating the tethers and fully characterize their biophysical properties via optical trapping.

Khalil, A.S. et al. Proc. Natl. Acad. Sci. USA 104, 4892–4897 (2007).

Imaging and visualization

Cell-penetrating quantum dots

Quantum dots are very popular probes for imaging owing to their broad adsorption range, narrow emission spectra and excellent photostability. Getting them into living cells is tricky, however, and even once in, they have a tendency to stay trapped in endosomes. Duan and Nie report the use of hyperbranched copolymer coatings to empower quantum dots with cell-penetrating and endosome-disrupting capabilities, which should facilitate their application for imaging in live cells.

Duan, H. & Nie, S. J. Am. Chem. Soc. 129, 3333–3338 (2007).