Stoichiometry and Topology in Protein Folding

Abstract

Crystals of the small ribosomal subunit from Thermus thermophilus diffract to 3Å and exhibit reasonable isomorphism and moderate resistance to irradiation. A 5Å MIR map of this particle shows a similar shape to the part assigned to this particle within the cryo-EM reconstructions of the whole ribosome and contains regions interpretable either as RNA chains or as protein motifs. To assist phasing at higher resolution we introduced recombinant methods aimed at extensive selenation for MAD phasing. We are focusing on several ribosomal proteins that can be quantitatively detached by chemical means. These proteins can be modified and subsequently reconstituted into depleted ribosomal cores. They also can be used for binding heavy atoms, by incorporating chemically reactive binding sites, such as -SH groups, into them. In parallel we are co-crystallizing the ribosomal particles with tailor made ligands, such as antibiotics or cDNA to which heavy-atoms have been attached or diffuse the latter compounds into already formed crystals.