Fig. 3. (a) CMPs B, C and D and their self-assembly into a heterotrimer. The axial salt bridges formed between Asp and Lys of CMPs B and C are shown. (b) Native MS spectra of CMPs B, C and D and an annealed 1 : 1 : 1 mixture of CMPs B, C and D (50 μM in 10 mM aq. NH4Ac at pH 7 and 25 °C). The most abundant peaks of CMP D correspond to acetate adducts: +2Ac (*) and +3Ac. (c) Thermal denaturation of a 1 : 1 : 3 mixture of CMPs B, C and D monitored by temperature-controlled native MS (100 μM in 10 mM aq. NH4Ac at pH 7, heating rate of 1 °C min–1) shows the unfolding of two coexisting homotrimeric D·D·D (green) and heterotrimeric B·C·D (orange) helices with Tm,MS = 52 °C (B·C·D), and Tm,MS = 55 °C (D·D·D).
