The new image

Caption: Mouse Dorsal Root Ganglion (DRG) culture stained for tubulin and imaged by confocal microscopy

Contributors: Robin P. Smith, Vance P. Lemmon

The new featured article

Why are there (only) twenty natural amino acids to build proteins from? Even though not based on a rigorously true statement (there are actually a few other rare amino acids besides the ‘canonical’ twenty), it is a nevertheless intriguing question. What’s so cool about twenty anyway? Twenty is certainly NOT one of the accepted symbolic numbers. Twenty is not nearly as cool and suggestive as say one, three, seven, thirteen, seventeen (Friday the 17th is the day of wretched luck in Italian lore, as opposed to the more common Friday the 13th), 666… Twenty does sound kind of square and uninteresting in comparison, doesn’t it? It’s a relatively small integer, yet pathetically far from being a prime number. The small symbolic numbers that most reverberate in lore all seem to be prime for some reason. Does anyone know the reason for this apparent preference? Any guesses?

What if we had more than twenty amino acid building blocks to assemble proteins from? Would we get super-proteins that would enable even Arnold Schwartzenegger to learn to act finally? Or big time CEOs get a sense of humor? How about a protein that would get Zinedine Zidane to finally admit his behavior was unforgivable? (By the way, 2006, what a number). Or would we just get a warning from Mother Nature not to get ahead of ourselves, with the new cyborg proteins proving a complete waste of perfectly good time? Well, many scientists have asked that question, and some have tried to give answers. Arguably the most accomplished and famous researcher in this field is Professor Peter Schultz of the Scripps Research Institute in La Jolla, California.

The newest featured protocol in Nature Protocols homepage has as its main author Professor Jason Chin, himself an ex-member of Schultz’s research lab (which I presume he joined as a post-doc). The protocol covers a procedure to achieve insertion of un-natural amino acids in proteins ‘expressed’ (produced) in eukaryotic cells (human cells are eukaryotic for instance). It details in particular the generation and genetic selection in yeast (yes, they’re eukaryotic organisms too) of a library of (mutated) enzymes that are ultimately able to insert site-specifically un-natural amino acids in proteins in response to the so-called amber stop codon that the researchers purposefully ‘add’ the protein’s codifying gene. For the record, the test un-natural amino acid referred to in the protocol is O-methyltyrosine. Pretty cool and thought-provoking stuff, I can assure you.

Alas in the protocol you won’t find too much along the lines of philosophical considerations on the significance of the number twenty when it comes to proteins, but if you are looking for somewhere to start in such a quest, this is as good a place to start as any. Well, at least we at Nature Protocols think so…

Thank you to Baldo Lucchese our resident expert and Great Dane for supplying the text for this section.

The Discussion Forum

We have recently had very helpful replies to questions posted a few weeks ago! Perhaps you have been waiting to find out the answers as well.

The one about the comet assay

The one about affinity purification of anti-peptide rabbit polyclonal antibodies

Ask Aunty Bron

What is the impact factor of Nature Protocols?

This is a very good question, and one that we get asked quite frequently. The short answer is that we don’t have an impact factor yet.

The slightly longer answer involves answering another question: “What is an impact factor?”

Impact Factor = (the total number of citations in indexed journals that a journal receives for articles published in the year after “the year of interest”) / (the number of citable articles published by the journal in “the year of interest”)

This means that a journal needs to be more than two years old to have an impact factor. Nature Protocols launched in June 2006.