Reshaping the folding energy landscape of human carbonic anhydrase II by a single point genetic mutation Pro237His

Lanosterol modulates proteostasis via dissolving cytosolic sequestosomes/aggresome-like induced structures

Sequestration of misfolded proteins into distinct cellular compartments plays a pivotal role in proteostasis and proteopathies. Cytoplasmic ubiquitinated proteins are sequestered by p62/SQSTM1 to deposit in sequestosomes or aggresome-like induced structures (ALIS). Most aggresome or ALIS regulators identified thus far are recruiters, while little is known about the disaggregases or dissolvers. In this research, we showed that lanosterol synthase and its enzymatic product lanosterol effectively reduced the number and/or size of sequestosomes/ALIS/aggresomes formed by endogenous proteins in the HeLa and HEK-293A cells cultured under both non-stressed and stressed conditions. Supplemented lanosterol did not affect the proteasome and autophagic activities, but released the trapped proteins from the p62-positive inclusions accompanied with the activation of HSF1 and up-regulation of various heat shock proteins. Our results suggested that the coordinated actions of disaggregation by lanosterol and refolding by heat shock proteins might facilitate the cells to recycle proteins from aggregates. The disaggregation activity of lanosterol was not shared by cholesterol, indicating that lanosterol possesses additional cellular functions in proteostasis regulation. Our findings highlight that besides protein modulators, the cells also possess endogenous low-molecular-weight compounds as efficient proteostasis regulators.

Structural Characterization of Native Proteins and Protein Complexes by Electron Ionization Dissociation-Mass Spectrometry

Mass spectrometry (MS) has played an increasingly important role in the identification and structural and functional characterization of proteins. In particular, the use of tandem mass spectrometry has afforded one of the most versatile methods to acquire structural information for proteins and protein complexes. The unique nature of electron capture dissociation (ECD) for cleaving protein backbone bonds while preserving noncovalent interactions has made it especially suitable for the study of native protein structures. However, the intra- and intermolecular interactions stabilized by hydrogen bonds and salt bridges can hinder the separation of fragments even with preactivation, which has become particularly problematic for the study of large macromolecular proteins and protein complexes. Here, we describe the capabilities of another activation method, 30 eV electron ionization dissociation (EID), for the top-down MS characterization of native protein-ligand and protein-protein complexes. Rich structural information that cannot be delivered by ECD can be generated by EID. EID allowed for the comparison of the gas-phase and the solution-phase structural stability and unfolding process of human carbonic anhydrase I (HCA-I). In addition, the EID fragmentation patterns reflect the structural similarities and differences among apo-, Zn-, and Cu,Zn-superoxide dismutase (SOD1) dimers. In particular, the structural changes due to Cu-binding and a point mutation (G41D) were revealed by EID-MS. The performance of EID was also compared to that of 193 nm ultraviolet photodissociation (UVPD), which allowed us to explore their qualitative similarities and differences as potential valuable tools for the MS study of native proteins and protein complexes.

Impact of the 237th residue on the folding of human carbonic anhydrase II

The deficiency of human carbonic anhydrase II (HCAII) has been recognized to be associated with a disease called CAII deficiency syndrome (CADS). Among the many mutations, the P237H mutation has been characterized to lead to a significant decrease in the activity of the enzyme and in the Gibbs free energy of folding. However, sequence alignment indicated that the 237th residue of CAII is not fully conserved across all species. The FoldX theoretical calculations suggested that this residue did not significantly contribute to the overall folding of HCAII, since all mutants had small ΔΔG values (around 1 kcal/mol). The experimental determination indicated that at least three mutations affect HCAII folding significantly and the P237H mutation was the most deleterious one, suggesting that Pro237 was important to HCAII folding. The discrepancy between theoretical and experimental results suggested that caution should be taken when using the prediction methods to evaluate the details of disease-related mutations.

Y65C missense mutation in the WW domain of the Golabi-Ito-Hall syndrome protein PQBP1 affects its binding activity and deregulates pre-mRNA splicing

The PQBP1 (polyglutamine tract-binding protein 1) gene encodes a nuclear protein that regulates pre-mRNA splicing and transcription. Mutations in the PQBP1 gene were reported in several X chromosome-linked mental retardation disorders including Golabi-Ito-Hall syndrome. The missense mutation that causes this syndrome is unique among other PQBP1 mutations reported to date because it maps within a functional domain of PQBP1, known as the WW domain. The mutation substitutes tyrosine 65 with cysteine and is located within the conserved core of aromatic amino acids of the domain. We show here that the binding property of the Y65C-mutated WW domain and the full-length mutant protein toward its cognate proline-rich ligands was diminished. Furthermore, in Golabi-Ito-Hall-derived lymphoblasts we showed that the complex between PQBP1-Y65C and WBP11 (WW domain-binding protein 11) splicing factor was compromised. In these cells a substantial decrease in pre-mRNA splicing efficiency was detected. Our study points to the critical role of the WW domain in the function of the PQBP1 protein and provides an insight into the molecular mechanism that underlies the X chromosome-linked mental retardation entities classified globally as Renpenning syndrome.