Design of SpAAP variants and analysis of their solubility.

(A) Domain organization of SpAAP and schematic representation of the deletion mutants analyzed in this study. (B, C) SDS-PAGE analysis of solubility of SpAAP variants produced in E. coli cells. Frozen cell pellets were handled at room temperature to separate the soluble and insoluble protein fractions. For each sample, total cell extracts (ET), soluble proteins (SOL) and insoluble proteins (INS) were extracted from the same amount of cells (0.12 OD600). (B) Samples from cells producing the wild-type protein (wt), the protein deleted of the N-terminal helix (Δα), the isolated β-propeller (Nter), the isolated catalytic domain (Cter). (C) Samples from cells producing the charge mutants K6A, E10A, R14A. The solubility profile of all single-charge mutants were similar and are not shown. MW: molecular weight marker.