Folding Mechanism and Aggregation Propensity of the KH0 Domain of FMRP and Its R138Q Pathological Variant

• Published in: International journal of molecular sciences Vol. 23; no. 20; p. 12178
• Main Authors: Santorelli, Daniele, Troilo, Francesca, Fata, Francesca, Angelucci, Francesco, Demitri, Nicola, Giardina, Giorgio, Federici, Luca, Catalano, Flavia, Di Matteo, Adele, Travaglini-Allocatelli, Carlo
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 12.10.2022; MDPI
• Subjects: Amyloid; amyloid fibrils; C-Terminus; Destabilization; Equilibrium; Experiments; Fibrillogenesis; FMRP; Folding; folding intermediate; folding mechanism; Fragile X syndrome; Helices; Homology; Intellectual disabilities; KH domains; Kinetics; Missense mutation; Mutation; Proteins; RNA-binding protein; Spectrum analysis
• ISSN: 1422-0067; 1661-6596; 1422-0067
• DOI: 10.3390/ijms232012178

The K-homology (KH) domains are small, structurally conserved domains found in proteins of different origins characterized by a central conserved βααβ “core” and a GxxG motif in the loop between the two helices of the KH core. In the eukaryotic KHI type, additional αβ elements decorate the “core” at the C-terminus. Proteins containing KH domains perform different functions and several diseases have been associated with mutations in these domains, including those in the fragile X mental retardation protein (FMRP). FMRP is an RNA-binding protein crucial for the control of RNA metabolism whose lack or mutations lead to fragile X syndrome (FXS). Among missense mutations, the R138Q substitution is in the KH0 degenerated domain lacking the classical GxxG motif. By combining equilibrium and kinetic experiments, we present a characterization of the folding mechanism of the KH0 domain from the FMRP wild-type and of the R138Q variant showing that in both cases the folding mechanism implies the accumulation of an on-pathway transient intermediate. Moreover, by exploiting a battery of biophysical techniques, we show that the KH0 domain has the propensity to form amyloid-like aggregates in mild conditions in vitro and that the R138Q mutation leads to a general destabilization of the protein and to an increased fibrillogenesis propensity.