Fig. 2: Single particle analysis of MFAP4 with Ca²⁺.

A Cryo-EM micrograph of MFAP4 with Ca²⁺ (scale bar 10 nm). Separate experiments were performed with two different MFAP4 purifications. B 2D-class averages of top/bottom and side views of MFAP4 particles used for reconstruction of initial 3D reference. 2.D classes were produced from particles extracted with a box size of 273.6 Å. C Top and side views of the D2 symmetry 3.55 Å resolution 3D cryo-EM map of MFAP4, D along with superimposed atomic model of Q37-A255 with integrative depiction of C34-Q36, and (E) the integrative atomic model (Q37-A255 resolved by cryo-EM map, intermolecular disulphide bonds between C34 interpreted from presented biochemical and mutagenesis evidence, positions of C34-Q36 were modelled to minimise deviation from the expected bond length and angle restrictions in Coot 0.9.8.8). The top tetramer is red with the dimer halves coloured light and dark shades of red. The bottom tetramer is coloured blue with dimer halves coloured light and dark shades of blue. F Intra-tetrameric interactions as seen from the top (green inset) and side view (orange inset) of subpanel E. G Inter-tetrameric interactions as seen from the side view (pink inset) of subpanel E. Cysteine residues are coloured yellow in all subpanels. Hydrogen bonds are depicted as dashed blue lines. Residues are coloured according to inter-chain distance (dark orange <2.5 Å, light orange <8.5 Å; see colour scale in F/G). Source data are provided as a Source Data file.