Protein Nanocontainers from Nonviral Origin: Testing the Mechanics of Artificial and Natural Protein Cages by AFM

Abstract

Self-assembling protein nanocontainers are promising candidates for an increasingly wide scope of purposes. Their applications range from drug delivery vehicles and imaging agents to nanocompartments for controlled enzymatic activity. In order to exploit their full potential in these different fields, characterization of their properties is vital. For example, their mechanical properties give insight into the stability of a particle as a function of their internal content. The mechanics can be probed by atomic force microscopy nanoindentation, and while this single particle method is increasingly used to probe material properties of viral nanocages, it has hardly been used to characterize nonviral nanocages. Here we report nanoindentation studies on two types of nonviral nanocontainers: (i) lumazine synthase from Aquifex aeolicus (AaLS), which naturally self-assembles into icosahedral cages, and (ii) the artificial protein cage O3-33 originating from a computational design approach. In addition, we tested particles that had been engineered toward improved cargo loading capacity and compared these nanocages in empty and loaded states. We found that the thermostable AaLS cages are stiffer and resist higher forces before breaking than the O3-33 particles, but that mutations affecting the size of AaLS particles have a dramatic effect on their structural stability. Furthermore, we show that cargo packaging can occur while maintaining the cage's mechanical properties.

Nucleation of Minerals: Precursors, Intermediates and Their Use in Materials Chemistry

“…(c) A comparison of (a) and (b), which are overlapped. The difference in the advance rate between the two [120] half-layer steps is clearly revealed.…”

“…Of course, the advance rates of the various steps increased with increasing supersaturation (Table 1). [120] "fast retreat" and "slow retreat" half-layer steps during dissolution showed "fast advance" and "slow advance" behaviors, respectively, during growth. In (d), a new one-layer step was formed because the front of the half-layer step with the fast advance rate caught up with that of the immediately underlying half-layer step with the slow advance rate.…”

“…The sector-shaped 2D nuclei were defined by half-layer steps parallel to [120], [120], and a curved step edge tangent to [010] (Figures 2 and 3). Such sector-shaped 2D nuclei have been formed in various supersaturated BaSO 4 solutions at room temperature {e.g., SI = 3 [8]; SI = 3.3 and 4.3 [18]; and SI = 4.0 and 4.5 [4]}.…”

“…For example, by (nano) indenting or stretching materials, their mechanical properties, such as adhesion and elasticity, can be precisely measured and mapped on the surface [100-104]. AFM-based nanoindentation and force spectroscopy has been applied to study many biological and bio-inspired systems, including bacterial adhesive material [105], viruses [106][107][108][109][110][111][112][113][114][115][116][117][118], proteins [119][120][121][122][123][124][125] In this review, a series of examples will be presented to illustrate the applications of in situ AFM and HS-AFM in the field of nucleation and self-assembly. These recent reports will be categorized into three groups based on their subjects: soft (E < 10 GPa) biogenic materials, soft bio-inspired materials, and hard (E > 10 GPa) materials.…”

In Situ Atomic Force Microscopy Studies on Nucleation and Self-Assembly of Biogenic and Bio-Inspired Materials

“…For example, by (nano) indenting or stretching materials, their mechanical properties, such as adhesion and elasticity, can be precisely measured and mapped on the surface [100][101][102][103][104]. AFM-based nanoindentation and force spectroscopy has been applied to study many biological and bio-inspired systems, including bacterial adhesive material [105], viruses [106][107][108][109][110][111][112][113][114][115][116][117][118], proteins [119][120][121][122][123][124][125], nucleic acids [126][127][128][129][130], cells [131][132][133], and plant cell walls [134]. The mechanical properties of the materials can be connected to the processes of material nucleation and self-assembly [100][101][102][103].…”