Label-Free Tracking of Hepatitis B Virus Core Protein Capsid Assembly in Real-Time Using Protein Charge Transfer Spectra.

Hepatitis B virions are double-shelled particles, with a diameter of 40-42 nm, consisting of a nucleocapsid called the HBV core protein (HBV Cp). It is an ordered assembly of 90-120 homodimers arranged in an icosahedral symmetry. Both the full-length HBV Cp and the first-149 residue domain, HBV Cp149, can spontaneously assemble in vitro into capsids with 120 Cp dimers ( = 4) or 90 Cp dimers ( = 3), triggered by high ionic strength of 0.

Early events during the aggregation of Aβ-derived switch-peptides tracked using Protein Charge Transfer Spectra.

Background: Understanding Aβ aggregation and inhibiting it at early stages is of utmost importance in treating Alzheimer's and other related amyloidogenic diseases. However, majority of the techniques to study Aβ aggregation mainly target the late stages; while those used to monitor early stages are either expensive, use extrinsic dyes, or do not provide information on molecular level interactions. Here, we investigate the early events of Aβ(KLVFFAE) aggregation using Aβ derived switch-peptides (SwPs) through a novel label-free approach employing Protein Charge Transfer Spectra (ProCharTS).

Protein charge transfer spectra in a monomeric protein with no lysine.

UV-Visible absorption and luminescence originating from non-aromatic groups in proteins is being intensely investigated today. Earlier work has shown that non-aromatic charge clusters in a folded monomeric protein can collectively act like a chromophore. Incident light in the near UV-Visible wavelength causes photoinduced electron transfer from the Highest Occupied Molecular Orbital (HOMO) of the electron-rich donor (like a carboxylate anion) to the Lowest Unoccupied Molecular Orbital (LUMO) of the electron-deficient acceptor (like a protonated amine or the polypeptide backbone) in the protein giving rise to absorption spectra in the 250-800 nm range referred to as Protein Charge Transfer Spectra (ProCharTS).

Role of Charged Amino Acids in Sullying the Fluorescence of Tryptophan or Conjugated Dansyl Probe in Monomeric Proteins.

When Trp/dansyl probe conjugated to a monomeric protein is photoexcited, it is assumed that all emitted fluorescence originates solely from them. In this work, we show that hidden unconventional intrinsic chromophores (called ProCharTS) that originate from confined charge clusters in the protein can contaminate Trp/dansyl emission. Previous work has shown that charge recombination among charge-separated excited states of monomeric proteins, rich in charged residues, can emit weak luminescence (300-700 nm) overlapping with ProCharTS absorption (250-800 nm) and Trp (300-400 nm) and dansyl (400-600 nm) emission.