Abstract
Symmetrical protein complexes are ubiquitous in biology. Many have been re-engineered for chemical and medical applications. Viral capsids and their assembly are frequent platforms for these investigations. A means to create asymmetric capsids may expand applications. Here, starting with homodimeric Hepatitis B Virus capsid protein, we develop a heterodimer, design a hierarchical assembly pathway, and produce asymmetric capsids. In the heterodimer, the two halves have different growth potentials and assemble into hexamers. These preformed hexamers can nucleate co-assembly with other dimers, leading to Janus-like capsids with a small discrete hexamer patch. We can remove the patch specifically and observe asymmetric holey capsids by cryo-EM reconstruction. The resulting hole in the surface can be refilled with fluorescently labeled dimers to regenerate an intact capsid. In this study, we show how an asymmetric subunit can be used to generate an asymmetric particle, creating the potential for a capsid with different surface chemistries.
Highlights
Symmetrical protein complexes are ubiquitous in biology
Hepatitis B Virus (HBV) capsid dimeric subunits can assemble two species of capsids, T = 3 capsid with 90 dimers and T = 4 capsid with 120 dimers
Using charge detection mass spectrometry (MS) (CDMS), a single-molecule native MS technique capable of resolving the masses of complex mixtures[47], we found that major species were free dimers, dimers of dimers, and hexamers with some putative 11-dimer double hexamers (Fig. 3b)
Summary
Symmetrical protein complexes are ubiquitous in biology. Many have been re-engineered for chemical and medical applications. The two halves have different growth potentials and assemble into hexamers These preformed hexamers can nucleate co-assembly with other dimers, leading to Janus-like capsids with a small discrete hexamer patch. Symmetrical subunits offer little or no opportunity to control the reaction and to incorporate specific asymmetric features. This shortcoming may limit development of applications that need conditional stops for information insertion and cargo loading. A dimer has two contact helices at either end[23,33,34] In concept, both monomers can be engineered differently, leading to a heterodimer for which each monomer can only assemble with other dimers in response to a specific condition. The chemically distinct nature of the two patches give us the ability to control further modification, disassembly, and reassembly
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