research papers
Since the introduction of structural genomics, the protein has been recognized as the most important variable in crystallization. Recent strategies to modify a protein to improve crystal quality have included rationally engineered point mutations, truncations, deletions and fusions. Five naturally occurring variants, differing in 1-18 amino acids, of the 177-residue lectin domain of the F17G fimbrial adhesin were expressed and purified in identical ways. For four out of the five variants crystals were obtained, mostly in non-isomorphous space groups, with diffraction limits ranging between 2.4 and 1.1 Å resolution. A comparative analysis of the crystal-packing contacts revealed that the variable amino acids are often involved in lattice contacts and a single amino-acid substitution can suffice to radically change crystal packing. A statistical approach proved reliable to estimate the compatibilities of the variant sequences with the observed crystal forms. In conclusion, natural variation, universally present within prokaryotic species, is a valuable genetic resource that can be favourably employed to enhance the crystallization success rate with considerably less effort than other strategies.
Keywords: crystallization; natural variation; prokaryotic diversity; adhesin; fimbriae; lectin domain.
Supporting information
PDB references: F17a-G–GlcNAc, 2bsc, r2bscsf; F17a-G–GlcNAc(β1-)OMe, 1zpl, r1zplsf; F17b-G–chitobiose, 2bs7, r2bs7sf; F17b-G–GlcNAc, 2bs8, r2bs8sf; F17e-G–GlcNAc, 2bsb, r2bsbsf; F17f-G–GlcNAc, 1zk5, r1zk5sf