Interrogating viral capsid assembly with ion mobility–mass spectrometry

Abstract

Most proteins fulfil their function as part of large protein complexes. Surprisingly, little is known about the pathways and regulation of protein assembly. Several viral coat proteins can spontaneously assemble into capsids in vitro with morphologies identical to the native virion and thus resemble ideal model systems for studying protein complex formation. Even for these systems, the mechanism for self-assembly is still poorly understood, although it is generally thought that smaller oligomeric structures form key intermediates. This assembly nucleus and larger viral assembly intermediates are typically low abundant and difficult to monitor. Here, we characterised small oligomers of Hepatitis B virus (HBV) and norovirus under equilibrium conditions using native ion mobility mass spectrometry. This data in conjunction with computational modelling enabled us to elucidate structural features of these oligomers. Instead of more globular shapes, the intermediates exhibit sheet-like structures suggesting that they are assembly competent. We propose pathways for the formation of both capsids.

Thermodynamic origins of protein folding, allostery, and capsid formation in the human hepatitis B virus core protein

“…Thus, there is a greater likelihood of seeing metastable species in ESI-IMS-MS. We cannot exclude the extra intermediate arising from a gas phase artifact or being present in solution (but unresolved). However, these possibilities seem unlikely because HBc 1-149 capsid assembly was studied in the gas phase and agreed well with solution data (47,48) and no additional intermediates were detected using CD, FES, and MST (Fig. 2).…”

Top-down proteomic analysis of protein pharmaceuticals, mixtures of protein complexes, and ribosomal protein extracts by capillary zone electrophoresis-mass spectrometry

“…For a variety of proteins and non-covalent protein complexes in the range of 15-500 kDa, Ω and R S were found to be closely-related, confirming that protein conformation is preserved during ESI [95]. Moreover, a growing body of evidence, obtained with a variety of techniques, confirms conformational similarity between protein structures in the condensed and gas phases [96][97][98][99][100][101][102][103][104].…”

Harnessing the power of microbial nanowires

“…The geometric assembly of proteins leads, for example, to the formation of molecular nanomachines and hyperstructures such as the ATP synthase complex and the cytoskeletal microtubules respectively (Alfaro‐Aco and Petry, 2015; Ruhle and Leister, 2015). Proteins can also self‐assemble in planar geometric configurations to make the S‐layer lattices of some bacteria and archaea (Sleytr et al ., 2014) and into distinctive 3D geometries such as bacterial intracellular microcompartments and viral capsids (Uetrecht et al ., 2011; Sutter et al ., 2017). These natural designs have inspired the synthesis of novel nanomaterials and protocols for protein functionalization and controlled association that modulate the material's properties and enable new functions (Yang et al ., 2016).…”