Insoluble protein purification with sarkosyl: facts and precautions

When eukaryotic proteins are overexpressed in Escherichia coli hosts, they often form inclusion bodies. Natively folded proteins can be extracted from inclusion bodies using mild detergents such as sarkosyl. One common problem is the sequestration of nucleic acid contaminants with the protein of interest. Here we describe methods for monitoring the presence of co-precipitated nucleic acids, and their removal. These procedures are simple to implement and can be easily adapted to a high-throughput format. While sarkosyl is a common chemical, some information such as its UV absorption spectrum and micellar size are absent in the literature or poorly referenced. We review and summarize the properties that are the most relevant to structural biology.