Toward the Reconstitution of a Two-Enzyme Cascade for Resveratrol Synthesis on Potyvirus Particles.

The highly ordered protein backbone of virus particles makes them attractive candidates for use as enzyme nano-carriers (ENCs). We have previously developed a non-covalent and versatile approach for adhesion of enzymes to virus particles. This approach makes use of z33, a peptide derived from the B-domain of Staphylococcus aureus protein A, which binds to the Fc domain of many immunoglobulins. We have demonstrated that with specific antibodies addressed against the viral capsid proteins (CPs) an 87% coverage of z33-tagged proteins can be achieved on potyvirus particles. 4-coumarate coenzyme A ligase (4CL2) and stilbene synthase (STS) catalyze consecutive steps in the resveratrol synthetic pathway. In this study, these enzymes were modified to carry an N-terminal z33 peptide and a C-terminal 6xHis tag to obtain (z)4CL2(His) and (z)STS(His), respectively. A protein chimera, (z)4CL2::STS(His), with the same modifications was also generated from the genetic fusion of both mono-enzyme encoding genes. All z33 enzymes were biologically active after expression in Escherichia coli as revealed by LC-MS analysis to identify resveratrol and assembled readily into macromolecular complexes with Potato virus A particles and α-PVA CP antibodies. To test simultaneous immobilization-purification, we applied the double antibody sandwich - ELISA protocol to capture active z33-containg mono-enzymes and protein chimera directly from clarified soluble cell lysates onto the virus particle surface. These immobilized enzymes were able to synthesize resveratrol. We present here a bottom up approach to immobilize active enzymes onto virus-based ENCs and discuss the potential to utilize this method in the purification and configuration of nano-devices.

Electrochemical atomic force microscopy imaging of redox-immunomarked proteins on native potyviruses: from subparticle to single-protein resolution.

We show herein that electrochemical atomic force microscopy (AFM-SECM), operated in molecule touching (Mt) mode and combined with redox immunomarking, enables the in situ mapping of the distribution of proteins on individual virus particles and makes localization of individual viral proteins possible. Acquisition of a topography image allows isolated virus particles to be identified and structurally characterized, while simultaneous acquisition of a current image allows the sought after protein, marked by redox antibodies, to be selectively located. We concomitantly show that Mt/AFM-SECM, due to its single-particle resolution, can also uniquely reveal the way redox functionalization endowed to viral particles is distributed both statistically among the viruses and spatially over individual virus particles. This possibility makes Mt/AFM-SECM a unique tool for viral nanotechnology.

Cotranslational coat protein-mediated inhibition of potyviral RNA translation.

UNLABELLED: Potato virus A (PVA) is a single-stranded positive-sense RNA virus and a member of the family Potyviridae. The PVA coat protein (CP) has an intrinsic capacity to self-assemble into filamentous virus-like particles, but the mechanism responsible for the initiation of viral RNA encapsidation in vivo remains unclear. Apart from virion assembly, PVA CP is also involved in the inhibition of viral RNA translation. In this study, we show that CP inhibits PVA RNA translation in a dose-dependent manner, through a mechanism involving the CP-encoding region. Analysis of this region, however, failed to identify any RNA secondary structure(s) preferentially recognized by CP, suggesting that the inhibition depends on CP-CP rather than CP-RNA interactions. In agreement with this possibility, insertion of an in-frame stop codon upstream of the CP sequence led to a marked decrease in the inhibition of viral RNA translation. Based on these results, we propose a model in which the cotranslational interactions between excess CP accumulating in trans and CP translated from viral RNA in cis are required to initiate the translational repression. This model suggests a mechanism for how viral RNA can be sequestered from translation and specifically selected for encapsidation at the late stages of viral infection. IMPORTANCE: The main functions of the CP during potyvirus infection are to protect viral RNA from degradation and to transport it locally, systemically, and from host to host. Although virion assembly is a key step in the potyviral infectious cycle, little is known about how it is initiated and how viral RNA is selected for encapsidation. The results presented here suggest that CP-CP rather than CP-RNA interactions are predominantly involved in the sequestration of viral RNA away from translation. We propose that the cotranslational nature of these interactions may represent a mechanism for the selection of viral RNA for encapsidation. A better understanding of the mechanism of virion assembly may lead to development of crops resistant to potyviruses at the level of viral RNA encapsidation, thereby reducing the detrimental effects of potyvirus infections on food production.

General strategy for ordered noncovalent protein assembly on well-defined nanoscaffolds.

Here we develop a novel approach allowing the noncovalent assembly of proteins on well-defined nanoscaffolds such as virus particles. The antibody-binding peptide Z33 was genetically fused to the monomeric yellow fluorescent protein and 4-coumarate:CoA-ligase 2. This Z33 "tag" allowed their patterning on the surface of zucchini yellow mosaic virus by means of specific antibodies directed against the coat protein of the virus. The approach was validated by affinity assays and correlative microscopy. The coverage efficiency was ≈ 87%. Fluorescence and enzymatic activity were fully retained after assembly. The principle of using the combination of a scaffold-specific antibody and Z33-fusion proteins can be extended to a wide variety of proteins/enzymes and antigenic scaffolds to support coupling for creating functional "biochips" with optical or catalytic properties.