Fig. 1. BRICHOS loop regions and loop-swap variants.

a Single subunit from the crystal structure of wt proSP-C BRICHOS trimers (PDB accession number: 2yad). The dotted line indicates the loop which is missing in the crystal structure and its core region is marked with a blue shadow. The sequence is labeled in increments from blue for polar to red for hydrophobic residues. b Wt Bri2 BRICHOS modeled by AlphaFold 2, where the loop core is labeled as in (a). c Amino acid sequences of human BRICHOS loop regions (see Supplementary Fig. 1 for alignment) color-coded as in (a, b). The BRICHOS domains studied herein are in bold, the motifs 1–3 are boxed and T206 is indicated with an arrow. d Schematic models of loop swap and delta loop variants. e SEC of BRICHOS oligomer variants (left) and estimated number of subunits (right). Number of subunits were estimated from the SEC peak maxima (indicated by center lines and numbers above boxes) and the boxes represent their full width at half maximum.