less than one Fab per dimer, whereby charge state resolution on theT=3 capsid is usually achieved at elevated collision voltages (CE). a more time-consuming cryo-electron microscopy analysis for preliminary characterisation of virus-antibody complexes. Keywords:Native MS, GEMMA, Hepatitis B, Virus-antibody complexes, Quasi-equivalence, Immune complex == Introduction == Hepatitis Ligustroflavone B computer virus (HBV) is a major cause of liver disease. In spite of the development of effective vaccines and antivirals for the prevention and treatment of HBV infections, the disease remains a serious health concern. Chronic contamination elicits production of large amounts of anti-capsid antibodies, motivating studies to better understand the conversation of the HBV capsid antigen with anti-capsid antibodies. In HBV capsids, the capsid protein (Cp) forms, both in vitro and in vivo, particles with two icosahedrally symmetric morphologies, Dnmt1 corresponding to the triangulation numbersT=4 andT=3 and consisting of 240 and 180 monomeric subunits, respectively [1]. Cp dimers are the building blocks for capsid formation and are stabilised by an intermolecular four-helix bundle and a disulphide bond within the bundle (Cys61) [24]. Together, these two capsids are known as the hepatitis B core antigen (HBcAg). At a structural level, conversation of HBcAg with a number of antibodies has been investigated, mainly by cryo-electron microscopy (cryo-EM) [511].T=4 capsids have four quasi-equivalent variants of each epitope (designated A, B, C, D) whereasT=3 capsids have only three (A, B, C), all present in 60 copies per capsid. Note, however, that similarly named sites (e.g. the B-epitope onT=3 and the B-epitope onT=4) are not necessarily equivalent [12]. Data show both, that epitopes are quite diverse and that there can be pronounced variations in binding affinity between quasi-equivalent variants of a given epitope. The majority of mapped epitopes exist as conformational discontinuous epitopes, although one conformational linear epitope and one non-conformational linear epitope have also been observed [13,14]. The locations of the majority of Ligustroflavone these epitopes have been mapped to the upper region of the four-helix bundle that constitutes the capsid spike. However, a distinct epitope has been recognized for the monoclonal antibody 3120 [15]. Characterisation by cryo-EM of Fab 3120-binding mapped its epitope to the floor region of the capsids, and pronounced differences in the occupancies of the seven quasi-equivalent variants of the epitope (from 0 to 100 %) were observed, reflecting differences in affinity arising from nuances in structure [15]. Since Fab 3120 detects, and has historically defined, the -epitope on HBcAg [5], it is generally used in diagnostic Ligustroflavone assays. Furthermore, the antibody is usually specific for put together capsids and does not bind to dimeric capsid subunits [16]. Among the human antibodies isolated from HBV clinical sera, Ligustroflavone some were shown to have a similar binding fingerprint [11], indicating that 3120-like antibodies are a major component of the anti-HBcAg response to HBV contamination. Following the introduction of electrospray ionisation [17], native mass spectrometry (MS) has emerged as a valuable technique for the characterisation of protein assemblies in terms of molecular excess weight (Mw), stoichiometry and structure. Application of this methodology to a variety of macromolecular systems, including viral particles [1821], heterogeneous protein assemblies [22,23] and membrane-bound protein assemblies [24], has demonstrated that many structural properties of large non-covalent protein complexes can be partially preserved in the gas phase. Ion mobility mass spectrometry (IMMS) has more recently been coupled to indigenous MS and produces additional information associated with size, charge and shape [2529]. Up coming to indigenous MS, gas-phase electrophoretic flexibility molecular evaluation (GEMMA) has surfaced alternatively solution to characterise macromolecular contaminants such as proteins complexes, virus-antibody and infections complexes [3038]. Both techniques commence with electrospray ionization (ESI) of proteins assemblies from a pseudophysiological buffer (e.g. aqueous ammonium acetate). In indigenous MS, the multiply billed ions that are created undergo intensive desolvation and so are consequently separated by mainly time-of-flight (ToF) mass analysers. In GEMMA, the original ESI process can be accompanied by charge manipulation that decreases the contaminants to singly billed ions that are separated by their electrophoretic flexibility size (EMD) at atmospheric pressure, which corresponds to particle size in the entire case of globular analytes. Finally, they may be recognized by vapour condensation for the separated billed contaminants with following laser beam light scattering [31 singly,39]. In this scholarly study, a mixture was utilized by us of ESI-based methods, GEMMA and MS, to probe the discussion of Fab 3120.