The protonation state of histidine 111 regulates the aggregation of the evolutionary most conserved region of the human prion protein

Abstract

In a group of neurodegenerative diseases, collectively termed transmissible spongiform encephalopathies, the prion protein aggregates into b-sheet rich amyloid-like deposits. Because amyloid structure has been connected to different prion strains and cellular toxicity, it is important to obtain insight into the structural properties of prion fibrils. Using a combination of solution NMR spectroscopy, thioflavin-T fluorescence and electron microscopy we here show that within amyloid fibrils of a peptide containing residues 108-143 of the human prion protein ]-the evolutionary most conserved part of the prion protein -residue H111 and S135 are in close spatial proximity and their interaction is critical for fibrillization. We further show that residues H111 and H140 share the same microenvironment in the unfolded, monomeric state of the peptide, but not in the fibrillar form. While protonation of H140 has little influence on fibrillization of humPrP (108-143), a positive charge at position 111 blocks the conformational change, which is necessary for amyloid formation of humPrP (108-143). Our study thus highlights the importance of protonation of histidine residues for protein aggregation and suggests point mutations to probe the structure of infectious prion particles.

Alanine Scanning Effects on the Biochemical and Biophysical Properties of Intrinsically Disordered Proteins: A Case Study of the Histidine to Alanine Mutations in Amyloid-β42

“…Alanine scanning has been widely used in studying the ligand and receptor interactions of intrinsically disordered proteins without considering how these artificial mutations may affect the biophysical and biochemical properties of query proteins (see, for example, refs − ). For instance, histidine to alanine mutations have been commonly utilized in the ligand and receptor interaction studies of amyloid-β 42 (Aβ 42 ). − The Aβ 42 peptide has three histidine (His) residues (His6, His13, and His14) in its primary structure, all located in the N-terminal half of this peptide (see below for the amino acid residue sequence).…”

“…Alanine scanning has been widely used in studying the ligand and receptor interactions of intrinsically disordered proteins without considering how these artificial mutations may affect the biophysical and biochemical properties of query proteins (see, for example, refs − ). For instance, histidine to alanine mutations have been commonly utilized in the ligand and receptor interaction studies of amyloid-β 42 (Aβ 42 ). − The Aβ 42 peptide has three histidine (His) residues (His6, His13, and His14) in its primary structure, all located in the N-terminal half of this peptide (see below for the amino acid residue sequence). While the mechanism of Aβ toxicity is poorly understood, it has previously been demonstrated that modifications of three His residues (His6, His13, and His14) of Aβ are able to modulate toxicity of this protein. , Furthermore, ligand and receptor interaction studies of Aβ 42 found that His residues bind to metal ligands, such as zinc, copper, cadmium, and iron ions. − These studies usually involve alanine scanning (mutation of His to Ala) for detailed investigations of the binding mechanisms between the ligand and receptor. − However, Aβ 42 is a rather short intrinsically disordered polypeptide that lacks stable two and three-dimensional (3D) structures and that exists as a highly dynamic conformational ensemble.…”

Unraveling the Histidine Tautomerism Effect on the Initial Stages of Prion Misfolding: New Insights from a Computational Perspective

“…51 In addition, previous research indicates that protonation of these two His amino acids affect PrP accumulation and fibril formation. 52,53 However, regarding the unprotonated conditions, there is still a lack of research on the impact of the tautomeric condition in neutral His residues in huPrP. As each His includes two tautomeric states (δ and ε), four isomeric forms exist in the present peptide chain (Table 1).…”

“…Although PrP has several His residues, a segment including His 140 (H140) and H155 was utilized for REMD in the current work, because these residues are important for PrP oligomerization and conformational transition. − Furthermore, H140 is already included in the highly accumulation-prone hot spot area of PrP (region 127–147) . In addition, previous research indicates that protonation of these two His amino acids affect PrP accumulation and fibril formation. , However, regarding the unprotonated conditions, there is still a lack of research on the impact of the tautomeric condition in neutral His residues in huPrP. As each His includes two tautomeric states (δ and ε), four isomeric forms exist in the present peptide chain (Table ).…”

High Susceptibility of Histidine to Charge Solvation Revealed by Cold Ion Spectroscopy

“…Protonated and neutral His residues in biomolecules should therefore exhibit very distinct spectroscopic signatures in the gas phase.Asolution-like UV absorption should indicate the lack of ac harge on aH is residue,while the redshifted absorption similar to that of HisH + in Figure 1p oints to al ikely protonation of the residue.A part from structural determination, charge state of His residues has important biological implications.For instance,recent studies evidence that charge states of buried His residues regulate misfolding of prion proteins toward their toxic forms and, ultimately,t heir aggregation to harmful amyloids. [23] Ac harge state of such buried His should not change upon desolvation and therefore can, potentially,b ed etermined in the gas phase from Hisspecific UV spectra, measured by monitoring His-specific photofragments (e.g., the loss of the His side chain). [3] In conclusion, the recorded UV photofragmentation spectrum of protonated histidine exhibits an unusual large redshift from its absorption in solution.…”