The morphogenic linker peptide of HBV capsid protein forms a mobile array on the interior surface

Abstract

Many capsid proteins have peptides that in¯uence their assembly. In hepatitis B virus capsid protein, the peptide STLPETTVV, linking the shell-forming`core' domain and the nucleic acid-binding`protamine' domain, has such a role. We have studied its morphogenic properties by permuting its sequence, substituting it with an extraneous peptide, deleting it to directly fuse the core and protamine domains and assembling core domain dimers with added linker peptides. The peptide was found to be necessary for the assembly of protamine domain-containing capsids, although its size-determining effect tolerates some modi®cations. Although largely invisible in a capsid crystal structure, we could visualize linker peptides by cryo-EM difference imaging: they emerge on the inner surface and extend from the capsid protein dimer interface towards the adjacent symmetry axis. A closely sequence-similar peptide in cellobiose dehydrogenase, which has an extended conformation, offers a plausible prototype. We propose that linker peptides are attached to the capsid inner surface as hinged struts, forming a mobile array, an arrangement with implications for morphogenesis and the management of encapsidated nucleic acid.

High-resolution mass spectrometry of viral assemblies: Molecular composition and stability of dimorphic hepatitis B virus capsids

“…Negative-staining EM was performed as described (11). These micrographs were used to determine the T ϭ 4 to T ϭ 3 ratio.…”

“…Both in vivo and in vitro, the capsid protein (cp) forms icosahedral capsids of two sizes, corresponding to triangulation numbers of T ϭ 3 and T ϭ 4 (6), nominally consisting of 180 and 240 subunits, respectively (7)(8)(9)(10). Cp has a 140-residue N-terminal core domain connected to a 34-residue ''protamine domain'' by a 10-residue linker (11). The protamine domain binds RNA, whereas the core domain is necessary and sufficient for capsid assembly.…”

Stability and Morphology Comparisons of Self-AssembledVirus-Like Particles from Wild-Type and Mutant Human Hepatitis B VirusCapsidProteins

“…10) (7, 31). The relative proportion between the smaller capsids with a triangulation number of Tϭ3 and the larger capsids with Tϭ4 is known to be influenced by a linker peptide of HBcAg at amino acids 141 to 149 (29,38). To date, it remains unknown whether other parts of the HBcAg molecule, such as amino acid 97, might influence the relative proportions between the two.…”

“…The Tϭ4 particles are the predominant fraction (Ͼ95%) when either full-length HBcAg1-183 or truncated HBcAg1-149 is expressed in E. coli. Interestingly, when the HBcAg1-140 version is expressed in E. coli, the predominant population of self-assembled icosahedral particles are Tϭ3 (29,38). Both larger and smaller particles can be found not only in the laboratory setting but also in human liver in natural infections (5,15).…”

A fusion product of the complete Borrelia burgdorferi outer surface protein A (OspA) and the hepatitis B virus capsid protein is highly immunogenic and induces protective immunity similar to that seen with an effective lipidated OspA vaccine formula

“…The icosahedral capsid, serologically defined as HBcAg, consists of 90 or 120 dimers [12,13] of a single capsid (core) protein species that is 183 aa in length. The first 140 aa are sufficient for particle assembly [14,15], and the basic C-terminal sequence acts as a nucleic acid binding domain [16]. A key structural feature of the dimer is a four-helix bundle [17] created from a helical hairpin in each monomer (Fig.…”