In vitro protein production is a very useful technique to quickly produce the protein of interest within a few days especially if your need s are for low amounts and you want to produce a variety of proteins or their modifications. Essentially, you mix the DNA template of interest with a cell extract. Incubate and isolate the protein that you want. Simple. The commercial companies have recognized their importance and there are many kits available from Invitrogen, New England Biolabs, Pierce and many others.
The extract that is used for this can be made from various sources with different characteristics. The simplest is an E.coli extract which is simple and cheap to make with high yield, quickly, and able to fold complex proteins. The wheat germ extract, is good for eukaryotic proteins and also gives high yields. The animal equivalent of eukaryotic is rabbit reticulocyte lysate which yields eukaryotic post-translational modifications. Recently, insect cell extracts are starting to be used which are good for eukaryotic post translational modification and signal sequences. The typical production that you would expect is about 1-2mg/ml of extract.
In 2009, Luo lab made an interesting observation. They found that using DNA hydrogel created by ligating branched DNA increased the production of protein by nearly 300 fold. The reason could be three fold: Th gel protects the template from nucleases probably through competition from within the gel, Template availability is higher since DNA gel protects the template DNA from denaturation or precipitation and third, the reaction occurs at a higher rate in small focal area’s within the matrix.
This could make a big difference in the use of in vitro technology but strangely has not been adopted as much by the industry. It could be that DNA gels require clean rooms and micromolds while being relatively more expensive. However, there is a probable business reason more than a scientific reason for this but worth investigating why new technologies take so long to mature and most of them don’t make any profit for their inventors.