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Domains and fusions
Protein yield
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Protein activity
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Toxic Protein

Protein Expression Technologies

Protein expression uses recombinant DNA technology to clone a protein coding DNA (cDNA) into a plasmid vector and express the protein in a host cell. However, several problems associated with protein expression in E. coli have been found.  The first obstacle is DNA cloning. Some protein coding cDNAs appear difficult to be cloned. Many can only be cloned in a vector with the wrong orientation. Some others contain mutations. Still others cannot be cloned in a particular vector at all. After a cDNA is cloned into a vector, the second problem is that the protein may not be expressed or the expression is inconsistent. Sometimes it is expressed at a low level, other times it is simply not expressed. Even after a successful expression, there may still be protein yield, solubility, stability and activity problems associated with the expressed protein. Therefore, many scientists claim that protein expression is an art rather than a science.

In a biological system, a particular protein is expressed only at a specific subcellular location in a t cell type of a tissue, during a defined time period, and at a particular level. This is the so called spatial, temporal, and quantitative expression. In a mammalian system, there are many different organs, tissues, and cell types. There may be over a million different cell types at different developmental stages in a human. Each protein in these cell types appears to be correctly expressed. Incorrect expressions often cause developmental defects or severe diseases. Some of the proteins are expressed at reasonably high levels such as antibodies in plasma cells and insulin in β cells in the islets of Langerhans of a pancreas. The only reasons that these cell types can correctly express these proteins are that these cells and their environment provide the necessary and sufficient materials and tools for the protein expressions.

There are several different types of expression host systems.  Each host system has its own advantages and disadvantages. In a given recombinant system, basic materials and tools for protein transcription and translation are provided for protein expression. This is why many recombinant proteins are successfully expressed in different host cells. However no host cell can provide all the materials and tools necessary and sufficient for all protein expressions. This is why many other proteins cannot be expressed in a particular tested host cell. Almost all cDNAs are first cloned in E.coli. E.coli is by far the most commonly used host for protein expression in research, diagnostic and pharmaceutical studies. It is the most studied organism in nature. The E.coli's relatively simple operations, low cost, high protein yield, short growth time, convenient expression control, and large selection of vectors and strains make it the number one choice in protein expression. Thus, our technologies and products are focused on DNA cloning and protein expression in E.coli system.

Expression Technologies Inc. is dedicated to providing scientific communities with the necessary and sufficient materials and tools for successful recombinant protein expression in E.coli.  There are different sections in our web site describing current technologies used in DNA cloning and protein expression. Host cells give protein expression advantages and disadvantages in each host system. Comparison of expression problems in different host systems are described in Problems and hosts. Decisions to express a recombinant protein as full-length, domains, large fusions or small tags are summarized in a table in Domain and fusion. Technologies to overcome difficulties in cDNA cloning and protein expression, that resulted from protein toxicity, are detailed in Toxic protein cloning and expression. Technologies to improve protein yield, solubility, stability, and activity are provided in Protein yield, Protein solubility, Protein stability, and Protein function sections respectively. Growth media are critically important in protein yield, solubility, stability, and activity. Therefore they are listed in a separate section. We also list some examples using our products to overcome DNA cloning and protein expression problems in each section. Our company mission is to provide scientists and the scientific community with the knowledge, products, and protocols necessary for successful DNA cloning and protein expression.


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