Mechanical disassembly of human picobirnavirus like particles indicates that cargo retention is tuned by the RNA–coat protein interaction

Abstract

Here we investigate the cargo retention of individual human picobirnavirus (hPBV) virus-like particles (VLPs) which differ in the N-terminal of their capsid protein (CP): (i) hPBV CP contains the full-length CP sequence; (ii) hPBV Δ45-CP lacks the first 45 N-terminal residues; and (iii) hPBV Ht-CP is the full-length CP with a N-terminal 36-residue tag that includes a 6-His segment. Consequently, each VLP variant holds a different interaction with the ssRNA cargo. We used atomic force microscopy (AFM) to induce and monitor the mechanical disassembly of individual hPBV particles. First, while Δ45-CP particles that lack ssRNA allowed a fast tip indentation after breakage, CP and Ht-CP particles that pack heterologous ssRNA showed a slower tip penetration after being fractured. Second, mechanical fatigue experiments revealed that the increased length in 8% of the N-terminal (Ht-CP) makes the virus particles to crumble ∼10 times slower than the wild type N-terminal CP, indicating enhanced RNA cargo retention. Our results show that the three differentiated N-terminal topologies of the capsid result in distinct cargo release dynamics during mechanical disassembly experiments because of the different interaction with RNA.