Isolation of Bacteria Envelope Proteins

Proteomic analysis on cell envelope proteins from Gram-negative bacteria requires specific isolation techniques. We found that conventional extraction methods such as osmotic shock cause extracts to be heavily contaminated with soluble cytoplasmic proteins. These cytoplasmic protein contaminants constitute the major signal in proteomic analysis and can overwhelm the signals coming from genuine envelope components. After extensive testing of various protocols for the preparation of envelope contents, we found that a modified version of the method of Oliver and Beckwith consistently produces the cleanest extract of periplasmic and outer membrane proteins. We have designated this very simple method TSE extraction because it uses a Tris-sucrose solution supplemented with
EDTA
. Cytoplasmic and inner membrane protein contaminants are not evident on 1D
SDS
polyacrylamide gels and contribute to less than 6% of total signal in very sensitive mass spectrometry analysis. This straightforward method is therefore ideal for �analyzing specific proteomic changes in the cell envelope.