title: Metamorphic proteins mediate evolutionary transitions of structure.
abstract: The primary sequence of proteins usually dictates a single tertiary and quaternary structure. However, certain proteins undergo reversible backbone rearrangements. Such metamorphic proteins provide a means of facilitating the evolution of new folds and architectures. However, because natural folds emerged at the early stages of evolution, the potential role of metamorphic intermediates in mediating evolutionary transitions of structure remains largely unexplored. We evolved a set of new proteins based on approximately 100 amino acid fragments derived from tachylectin-2--a monomeric, 236 amino acids, five-bladed beta-propeller. Their structures reveal a unique pentameric assembly and novel beta-propeller structures. Although identical in sequence, the oligomeric subunits adopt two, or even three, different structures that together enable the pentameric assembly of two propellers connected via a small linker. Most of the subunits adopt a wild-type-like structure within individual five-bladed propellers. However, the bridging subunits exhibit domain swaps and asymmetric strand exchanges that allow them to complete the two propellers and connect them. Thus, the modular and metamorphic nature of these subunits enabled dramatic changes in tertiary and quaternary structure, while maintaining the lectin function. These oligomers therefore comprise putative intermediates via which beta-propellers can evolve from smaller elements. Our data also suggest that the ability of one sequence to equilibrate between different structures can be evolutionary optimized, thus facilitating the emergence of new structures.
authors.affiliation: Department of Biological Chemistry, and Israel Structural Proteomics Center, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Itamar
authors.initials: I
authors.lastname: Yadid
authors.forename: Noam
authors.initials: N
authors.lastname: Kirshenbaum
authors.forename: Michal
authors.initials: M
authors.lastname: Sharon
authors.forename: Orly
authors.initials: O
authors.lastname: Dym
authors.forename: Dan S
authors.initials: DS
authors.lastname: Tawfik
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D001703:Biophysics / Q000379:methods; D019143:Evolution, Molecular; D006023:Glycoproteins / Q000737:chemistry; D037102:Lectins / Q000737:chemistry*; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid
chemical_list: D000596:Amino Acids; D006023:Glycoproteins; D037102:Lectins; D011506:Proteins