Fig. 5.

HSP18.1 forms a remarkably disperse range of complexes with Luc A Size exclusion chromatogram of a 1∶1 incubation of HSP18.1 and Luc, showing a peak at long elution times corresponding to HSP18.1 dodecamer, and a broad peak at shorter elution times corresponding to complexes between sHSP and client (see also Fig. S4). A fraction corresponding to the low-mass end of the complexes, bracketed, was chosen for MS analysis. B Histograms and fits for the abundance of the different complexes for the fraction determined from tandem-MS experiments. Overlaid is the fit to the distribution obtained in Fig. 3C (Black). Complexes are composed of a variable number of both sHSP and client. C Extrapolating the tandem-MS-derived distributions according to the SEC data reveals the distribution of all HSP18.1:Luc complexes formed at a 1∶1 incubation. Experimentally identified complexes are ringed. Over 300 complexes of over 1% relative intensity are thus observed, revealing a remarkable heterogeneity in the stoichiometries of interaction between sHSPs and clients.