A comparative analysis of the three most common strategies for isolating peptides with attached phosphates is presented online this week in Nature Methods.
The enzymatic addition and removal of phosphate groups on proteins is a crucial part of many biological processes, and it is therefore important to identify the phosphorylation sites where this occurs. Several strategies have been described for isolating phosphorylated peptides for subsequent analysis, but so far there has been no consensus on which method is 'best'. Ruedi Aebersold and colleagues found that three popular methods isolated partially overlapping, yet somewhat different sets of phosphorylated peptides from cells. They concluded that no single isolation method is currently sufficient for a comprehensive analysis of the 'phosphoproteome' - the total population of phosphorylated proteins in a given sample.
This finding should help the research community design more effective large-scale experiments to discover and analyze phosphorylated proteins in biological samples.
A method to regrow teeth
Nature Methods
A report to be published in the March issue of Nature Methods describes the first successful replacement of natural teeth in a mouse with teeth that were created in a Petri dish from single cells.
Takashi Tsuji and colleagues started with the two cell types that develop into a tooth, mesenchymal and epithelial cells; they first grew each cell type separately to get larger quantities of cells and then injected them into a drop of collagen, a substance ‘gluing’ cells together in an organism. The cells developed into a budding tooth with high efficiency, and when transplanted into the cavity of an extracted tooth in a mouse they developed normally and showed the same composition and structure as normal teeth.
The authors provide further evidence that this method can be applied to any organ that develops from these mesenchymal and epithelial cell types by regrowing a follicle that eventually forms a whisker in a mouse.
CONTACT
Takashi Tsuji (Tokyo University of Science, Faculty of Industrial Science and Technology, 2641 Yamazaki, Noda, Chiba 278-8510, Japan)
Tel: +81-4-7122-9711; E-mail: t-tsuji@nifty.com
Proteins a la carte
Nature Methods
A method to incorporate non-naturally occurring amino acids into proteins in mammalian cells is to be published online this week in Nature Methods. This is the first time the process has been successfully accomplished in mammalian cells and will allow scientists to ‘custom make’ proteins with new chemical properties useful for research, industry and medicine.
Protein synthesis is a three-step process in which the information encoded on the DNA is translated into a string of amino acids; first DNA is transcribed to mRNA, then enzymes - aminoacyl-tRNA synthetases - match each of the twenty naturally occurring amino acids with its corresponding transfer RNA (tRNA). The tRNAs then read the sequence on the mRNA and incorporate amino acids in the correct order into the growing protein.
Peter Schultz and colleagues changed an aminoacyl-tRNA synthetase in such a way that it paired the tRNA normally recognizing a stop codon - a sequence that terminates protein synthesis - with an unnatural amino acid. Instead of terminating protein synthesis this tRNA now incorporates an unnatural amino acid into the protein with high fidelity and efficiency and without being toxic for the cells.
CONTACT
Peter Schultz (Scripps Research Institute, La Jolla, CA, USA)
Tel: +1 858 784 9300; E-mail: schultz@scripps.edu
ADDITIONAL INFORMATION:
Michael Ibba (Ohio State University, Columbus, OH, USA)
Tel: +1 614 292 2120; E-mail: ibba.1@osu.edu
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