KTKEGV repeat motifs are key mediators of normal α-synuclein tetramerization: Their mutation causes excess monomers and neurotoxicity.
| Publication Type | Academic Article |
| Authors | Dettmer U, Newman A, von Saucken V, Bartels T, Selkoe D |
| Journal | Proc Natl Acad Sci U S A |
| Volume | 112 |
| Issue | 31 |
| Pagination | 9596-601 |
| Date Published | 07/07/2015 |
| ISSN | 1091-6490 |
| Keywords | Mutation, Neurons, Protein Multimerization, Repetitive Sequences, Amino Acid, alpha-Synuclein |
| Abstract | α-Synuclein (αS) is a highly abundant neuronal protein that aggregates into β-sheet-rich inclusions in Parkinson's disease (PD). αS was long thought to occur as a natively unfolded monomer, but recent work suggests it also occurs normally in α-helix-rich tetramers and related multimers. To elucidate the fundamental relationship between αS multimers and monomers in living neurons, we performed systematic mutagenesis to abolish self-interactions and learn which structural determinants underlie native multimerization. Unexpectedly, tetramers/multimers still formed in cells expressing each of 14 sequential 10-residue deletions across the 140-residue polypeptide. We postulated compensatory effects among the six highly conserved and one to three additional αS repeat motifs (consensus: KTKEGV), consistent with αS and its homologs β- and γ-synuclein all forming tetramers while sharing only the repeats. Upon inserting in-register missense mutations into six or more αS repeats, certain mutations abolished tetramer formation, shown by intact-cell cross-linking and independently by fluorescent-protein complementation. For example, altered repeat motifs KLKEGV, KTKKGV, KTKEIV, or KTKEGW did not support tetramerization, indicating the importance of charged or small residues. When we expressed numerous different in-register repeat mutants in human neural cells, all multimer-abolishing but no multimer-neutral mutants caused frank neurotoxicity akin to the proapoptotic protein Bax. The multimer-abolishing variants became enriched in buffer-insoluble cell fractions and formed round cytoplasmic inclusions in primary cortical neurons. We conclude that the αS repeat motifs mediate physiological tetramerization, and perturbing them causes PD-like neurotoxicity. Moreover, the mutants we describe are valuable tools for studying normal and pathological properties of αS and screening for tetramer-stabilizing therapeutics. |
| DOI | 10.1073/pnas.1505953112 |
| PubMed ID | 26153422 |
| PubMed Central ID | PMC4534262 |