Thermal Stability of RNA Phage Virus-Like Particles Displaying Foreign Peptides

Jerri C Caldeira,David S Peabody

doi:10.1186/1477-3155-9-22

Abstract

BackgroundTo be useful for genetic display of foreign peptides a viral coat protein must tolerate peptide insertions without major disruption of subunit folding and capsid assembly. The folding of the coat protein of RNA phage MS2 does not normally tolerate insertions in its AB-loop, but an engineered single-chain dimer readily accepts them as long as they are restricted to one of its two halves.ResultsHere we characterize the effects of peptide insertions on the thermal stabilities of MS2 virus-like particles (VLPs) displaying a variety of different peptides in one AB-loop of the coat protein single-chain dimer. These particles typically denature at temperatures around 5-10°C lower than unmodified VLPs. Even so, they are generally stable up to about 50°C. VLPs of the related RNA phage PP7 are cross-linked with intersubunit disulfide bonds and are therefore significantly more stable. An AB-loop insertion also reduces the stability of PP7 VLPs, but they only begin to denature above about 70°C.ConclusionsVLPs assembled from MS2 single-chain dimer coat proteins with peptide insertions in one of their AB-loops are somewhat less stable than the wild-type particle, but still resist heating up to about 50°C. Because they possess disulfide cross-links, PP7-derived VLPs provide an alternate platform with even higher stability.

Highlights

To be useful for genetic display of foreign peptides a viral coat protein must tolerate peptide insertions without major disruption of subunit folding and capsid assembly
We recently described a method for peptide presentation on virus-like particles (VLPs) of the RNA bacteriophage MS2, which we believe offers several advantages over other display systems for certain applications [1,2,3]
The bacteriophage MS2 coat protein is the major structural protein of the virus and when expressed from a plasmid in E. coli it self-assembles into VLPs whose shell structure is virtually identical to that of the MS2 virion

Summary

Introduction

To be useful for genetic display of foreign peptides a viral coat protein must tolerate peptide insertions without major disruption of subunit folding and capsid assembly. The folding of the coat protein of RNA phage MS2 does not normally tolerate insertions in its AB-loop, but an engineered single-chain dimer readily accepts them as long as they are restricted to one of its two halves. Like the filamentous phage display technique, MS2 VLP display should be useful for the affinity selection of peptides with binding activity for a wide variety of receptor molecules (e.g. antibodies). MS2 VLPs readily display foreign peptides at such high densities that they are strongly immunogenic. We are exploiting this capability to develop a vaccine discovery technology in which a single particle serves both for epitope identification and immunization [2,4]. The ability to present affinity-selected peptides to the immune system in the same structural context present during their affinity selection may facilitate the isolation of mimotopes able to elicit a desired antibody response [5,6]

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Conclusion