Fig. 3.

Identification and quantification of HSP18.1:Luc complexes by means of tandem-MS. A Spectrum of a complex formed between HSP18.1 and Luc at a 1∶0.1 ratio. Unbound dodecamer is observed around 6,350 m/z, and a broad area of signal, characteristic of a polydisperse ensemble, is observed above 8,000 m/z. B Selection of ions at a particular m/z, gray, and activation of selected ions leads to the removal of highly charged HSP18.1 subunits (≈1,800 m/z) from the parent oligomers. Complementary stripped complexes appear at high m/z, sufficiently separated that they can be assigned unambiguously (Fig. S6). C Relative quantification of the different complexes from the heights of the peaks reveals a number of different stoichiometries of HSP18.1 bound to one Luc, and a dominance (p < 0.01) of those containing an even number of HSP18.1 subunits relative to a Gaussian distribution. This saw-tooth pattern mirrors that observed when HSP18.1 is heated on its own, (Fig. 1C), revealing the importance of temperature controlled dynamics of the sHSP in complex formation. Data and error bars represent the mean and standard deviation of three experiments.