Detection of membrane protein-therapeutic agent complexes by mass spectrometry

A method of detecting a complex comprising a membrane protein bound to a therapeutic agent by mass spectrometry, wherein the method comprises:

• (a) providing a solution comprising a detergent micelle in which said complex is contained, wherein the detergent is present in the solution at a concentration which is greater than or equal to the critical micelle concentration of the detergent, and wherein the solution comprises a mass spectrometry compatible buffer;
• (b) providing a mass spectrometer comprising a nanoelectrospray ionisation source, a mass analyser and a detector;
• (c) vaporising the solution using the nanoelectrospray ionisation source under conditions such that the complex is released from the micelle;
• (d) ionising the complex;
• (e) resolving the ionised complex using the mass analyser;
• and
• (f) detecting the resolved complex using the detector, wherein the mass spectrometer is operated under one or more of the following conditions:
• (i) the capillary voltage of the nanoelectrospray ionisation source is from about 0.8 to about 2.2 kV;
• (ii) the cone voltage of the nanoelectrospray ionisation source is from about 80 to about 240 V;
• (iii) the trap collision energy is from about 80 to about 240 V;
• (iv) the source temperature is from about 0 to about 50° C.;
• (v) the bias voltage is from about 40 to about 200 V;
• and (vi) the backing pressure is from about 1 to about 8 mBar.