Improvement of Modular Protein Display Efficiency in SpyTag-Implemented Norovirus-like Particles

Self-Assembling protein nanoparticle platform for multivalent antigen delivery in vaccine development

Nanoparticle vaccines can efficiently and repeatedly display multivalent antigens, thereby improving the targeted delivery of antigens and inducing more durable immune responses, making them an important representative of novel vaccines. The global COVID-19 pandemic has accelerated the development of nanoparticle vaccines, offering a promising solution for the prevention and control of infectious diseases. Currently, the development of nanoparticle vaccines involves the use of various types of nanoparticles, including liposomes, polymers, inorganic materials, and emulsions. Protein nanoparticles candidate vaccines are attracting increasing attention because of their unique antigen presentation methods and self-assembly characteristics during their development, leading to a broad consensus on their promising future. Naturally self-assembling protein nanoparticles, such as ferritin, enhance antigen presentation, which aids in the activation of both humoral and cellular immune responses. This has led to significant advancements in the study of hepatitis B virus. Meanwhile, some synthetically engineered protein nanoparticles, such as mi3, and I53-50, can induce higher antibody titers through chemical conjugation with the SpyTag-SpyCatcher system, thereby providing better immunoprotection and showing promising prospects in the prevention of H1N1 and H3N2 influenza virus infections. This article reviews the unique advantages of protein nanoparticles as antigen delivery platforms, progress made in immunological design mechanisms, advances in the application of related adjuvants in preclinical and clinical trials, and the performance of commonly used computationally designed protein nanoparticles in preclinical trials, with a particular emphasis on the progress in the application of cationic nanoparticle vaccines. The aim is to provide future researchers with effective adjuvant strategies and high-quality selections for computationally designed protein nanoparticles, thereby promoting the clinical trial process of protein nanoparticles vaccines.

Modular Display of Plasmodium yoelii Circumsporozoite Surface Protein and Merozoite Surface Protein-1 on Norovirus-like Particles

Recently, virus-like particles have been regarded as a promising platform for displaying foreign peptides or proteins on their surface. In this study, a dual-protein-displaying platform based on the norovirus-like particle (NoV-LP) was developed using SpyTag (SpT)/SpyCatcher (SpC) protein bioconjugation. A short 14-amino-acid SpT peptide was added to the C-terminus of VP1, with a rigid "EAAAK" spacer in between. Antigenic proteins from a rodent malaria parasite, Plasmodium yoelii, specifically the circumsporozoite protein (PyCSP) and the 19 kDa C-terminal region of merozoite surface protein 1 (PyMSP119), were displayed on the surface of NoV-LPs in both monovalent and bivalent formats. The immunogenicity of these VLP-based vaccines was assessed, and they were found to induce antigen-specific IgG responses against both PyCSP and PyMSP119 in BALB/c mice in the absence of an adjuvant, at levels comparable to those induced by subunit antigenic proteins with an alum adjuvant added. Interestingly, the bivalent vaccine raised IgG responses at a similar titer to the monovalent vaccine. This finding hints that the NoV-LP possesses an inherent adjuvanted property in the presence of a foreign antigen. The measured anti-PyCSP and anti-PyMSP119 antibodies through ELISA indicate that surface display of PyCSP and PyMSP119 on SpTagged-NoV-LP has the potential for further development as a bivalent vaccine against two different life-cycle stages of malaria.

Keeping the Distance: Activity Control in Solid-Supported Sucrose Phosphorylase by a Rigid α-Helical Linker of Tunable Spacer Length

Enzyme immobilization into carrier materials has broad importance in biotechnology, yet understanding the catalysis of enzymes bound to solid surfaces remains challenging. Here, we explore surface effects on the catalysis of sucrose phosphorylase through a fusion protein approach. We immobilize the enzyme via a structurally rigid α-helical linker [EA3K] n of tunable spacer length due to the variable number of pentapeptide repeats used (n = 6, 14, 19). Molecular modeling and simulation approaches delineate the conformational space sampled by each linker relative to its His-tag cap used for surface tethering. The population distribution of linker conformers gets broader, with a consequent shift of the enzyme-to-surface distance to larger values (≤15 nm), as the spacer length increases. Based on temperature kinetic studies, we obtain an energetic description of catalysis by the enzyme-to-linker fusions in solution and immobilize on Ni2+-chelate agarose. The solid-supported enzymes involve distinct changes in enthalpy-entropy partitioning within the frame of invariant Gibbs free energy of activation (ΔG ‡ = ∼61 kJ/mol at 30 °C). The entropic contribution (-TΔS ‡) to ΔG ‡ increases with the spacer length, from -16.4 kJ/mol in the linker-free enzyme to +7.9 kJ/mol in the [EA3K]19 linked fusion. The immobilized [EA3K]19 fusion protein is indistinguishable in its catalytic properties from the enzymes in solution, which behave identically regardless of their linker. Enzymes positioned closer to the surface arguably experience a higher degree of molecular organization ("rigidification") that must relax for catalysis through the additional uptake of heat, compensated by a gain in entropy. Increased thermostability of these enzymes (up to 2.8-fold) is consistent with the proposed rigidification effect. Collectively, our study reveals surface effects on the activation parameters of sucrose phosphorylase catalysis and shows their consistent dependence on the length of the surface-tethering linker. The fundamental insight here obtained, together with the successful extension of the principle to a different enzyme (nigerose phosphorylase), suggests that rigid linker-based control of the protein-surface distance can be used as an engineering strategy to optimize the activity characteristics of immobilized enzymes.

Research progress of multi-enzyme complexes based on the design of scaffold protein

Multi-enzyme complexes designed based on scaffold proteins are a current topic in molecular enzyme engineering. They have been gradually applied to increase the production of enzyme cascades, thereby achieving effective biosynthetic pathways. This paper reviews the recent progress in the design strategy and application of multi-enzyme complexes. First, the metabolic channels in the multi-enzyme complex have been introduced, and the construction strategies of the multi-enzyme complex emerging in recent years have been summarized. Then, the discovered enzyme cascades related to scaffold proteins are discussed, emphasizing on the influence of the linker on the fusion enzyme (fusion protein) and its possible mechanism. This review is expected to provide a more theoretical basis for the modification of multi-enzyme complexes and broaden their applications in synthetic biology.

SpyTag/SpyCatcher display of influenza M2e peptide on norovirus-like particle provides stronger immunization than direct genetic fusion

Introduction

Virus-like particles (VLPs) are similar in size and shape to their respective viruses, but free of viral genetic material. This makes VLP-based vaccines incapable of causing infection, but still effective in mounting immune responses. Noro-VLPs consist of 180 copies of the VP1 capsid protein. The particle tolerates C-terminal fusion partners, and VP1 fused with a C-terminal SpyTag self-assembles into a VLP with SpyTag protruding from its surface, enabling conjugation of antigens via SpyCatcher.

Methods

To compare SpyCatcher-mediated coupling and direct peptide fusion in experimental vaccination, we genetically fused the ectodomain of influenza matrix-2 protein (M2e) directly on the C-terminus of norovirus VP1 capsid protein. VLPs decorated with SpyCatcher-M2e and VLPs with direct M2 efusion were used to immunize mice.

Results and discussion

We found that direct genetic fusion of M2e on noro-VLP raised few M2e antibodies in the mouse model, presumably because the short linker positions the peptide between the protruding domains of noro-VLP, limiting its accessibility. On the other hand, adding aluminum hydroxide adjuvant to the previously described SpyCatcher-M2e-decorated noro-VLP vaccine gave a strong response against M2e. Surprisingly, simple SpyCatcher-fused M2e without VLP display also functioned as a potent immunogen, which suggests that the commonly used protein linker SpyCatcher-SpyTag may serve a second role as an activator of the immune system in vaccine preparations. Based on the measured anti-M2e antibodies and cellular responses, both SpyCatcher-M2e as well as M2e presented on the noro-VLP via SpyTag/Catcher show potential for the development of universal influenza vaccines.