Conversion of a β‐strand to anα‐helix induced by a single‐site mutation observed in the crystal structure of fis mutant pro²⁶Ala

Abstract

The conversion from an a-helix to a P-strand has received extensive attention since this structural change may induce many amyloidogenic proteins to self-assemble into fibrils and cause fatal diseases. Here we report the conversion of a peptide segment from a P-strand to an a-helix by a single-site mutation as observed in the crystal structure of Fis mutant Pro26Ala determined at 2.0 8, resolution. Pro26 in Fis occurs at the point where a flexible extended P-hairpin arm leaves the core structure. Thus it can be classified as a "hinge proline" located at the C-terminal end of the P2-strand and the N-terminal cap of the A a-helix. The replacement of Pro26 to alanine extends the A a-helix for two additional turns in one of the dimeric subunits; therefore, the structure of the peptide from residues 22 to 26 is converted from a P-strand to an a-helix. This result confirms the structural importance of the proline residue located at the hinge region and may explain the mutant's reduced ability to activate Hin-catalyzed DNA inversion. The peptide (residues 20 to 26) in the second monomer subunit presumably retains its P-strand conformation in the crystal; therefore, this peptide shows a "chameleon-like'' character since it can adopt either an a-helix or a P-strand structure in different environments. The structure of Pro26Ala provides an additional example where not only the protein sequence, but also non-local interactions determine the secondary structure of proteins.

An analysis of the helix-to-strand transition between peptides with identical sequence

“…For example, a strand has been converted to a helix by the introduction of single point mutations. 58,59 Likewise, a helical 4-mer was caused to become part of a loop with the insertion of four residues in T4 lysozyme. 60 Thus, alternate structures can be induced by minor sequence change, and while intrinsic sequence properties can be important for structure formation, these preferences can be forgone to satisfy the structure of the molecule as a whole.…”

A folding space odyssey

“…It does seem clear, however, that most of the well established mechanisms of gene evolution, such as deletion/insertion, nonhomologous recombination, and gene duplication, do come into play (2,4 The possibility that limited changes in a protein fold can be induced by one or only a few substitutions has been demonstrated in several studies (12)(13)(14). For example, two substitutions in the N-terminal ␤-strand of the Arc repressor convert this region into a right-handed helix (12).…”

Data Mining the Protein Data Bank to Identify and Characterise Chameleon Coil Sequences that Form Symmetric Homodimer β-Sheet Interfaces

“…As winners of the Paracelsus challenge [18] have shown, a limited number of mutations can dramatically change a protein conformation: a protein which adopts a four helix conformation was designed while retaining 50% identity of a predominantly β-sheet protein [5]. Similarly, it was demonstrated that mutation of a single amino acid could be sufficient to convert a β-strand into an α-helix [23]. In addition to mutations, a protein's environment may also affect its secondary structure.…”