Fig. 3

Domain swapping in L2MN and L3MN. a Size exclusion profiles of L2MN, L2MN*, L3MN, and L3MN* at pH 7, are shown. L2MN* and L3MN* are variants of L2MN and L3MN respectively, in which the QVVAG sequence was mutated to QVNAG. Elution volumes corresponding to the dimeric and monomeric species are indicated. b The experimental SAXS data for the L2MN dimer is shown against the calculated scattering curves for the L2MN domain-swapped dimer based on a structural model derived from symmetrized-SBM simulations of L2MN, and for the wt MNEI crystal-contact dimer (PDB ID: 1IV7). c ¹⁵N-HSQC spectra of L3MN monomer (blue) and dimer (red) align well for most resonances, indicating that their overall folds are similar. d Chemical shift perturbation (CSP) between the L3MN monomer and dimer is shown for each residue. A weighted chemical shift difference (¹H and ¹⁵N) is plotted. For reference, the secondary structural arrangement of MNEI is indicated on the top. e The experimental SAXS data for the L3MN dimer is shown against calculated scattering curves for the L3MN domain-swapped dimer based on simulated models, and for the wt MNEI crystal-contact dimer (PDB ID: 1IV7). f Size exclusion profiles of wt MNEI, L1MN, L2MN, and L3MN are shown. Elution volumes corresponding to the monomeric and dimeric species are indicated. The fraction of the total protein that exists as a domain swapped dimer increases as the length of the target loop decreases (see Discussion). The total area under the elution peaks for each variant is comparable to the area under the elution peak for wt MNEI. Source data are provided as a Source Data file