The use of native gels for the concomitant determination of protein sequences and modifications by mass spectrometry with subsequent conformational and functional analysis of native proteins following electro-elution

The protocol consists of running a native gel with in-gel digestion by proteases, subsequent mass spectrometrical determination of protein sequence and modifications, followed by electro-elution and conformational analysis using melting point and circular dichroism. Finally, the eluted protein is tested for preserved function. Herein, C1 esterase inhibitor is applied on a native gel; in-gel digestion by proteases is carried out and peptides are identified by nano-LC-ESI-CID/ETD-MS/MS using an ion trap for generation of peptide sequences and protein modifications. Protein from replicate bands from the same gel is electro-eluted and used for determination of the melting point and used for circular dichroism analysis. Additional bands from the native gel are either in-gel digested with asparaginase to generate deamidation or PNGase F for deglycosylation, followed by mass spectrometry, conformational and functional studies. Preserved conformation and function of the C1 esterase inhibitor was shown. This protocol can be completed in 1 week.