Protein Nanotubes: From Bionanotech towards Medical Applications

Abstract

Nanobiotechnology involves the study of structures found in nature to construct nanodevices for biological and medical applications with the ultimate goal of commercialization. Within a cell most biochemical processes are driven by proteins and associated macromolecular complexes. Evolution has optimized these protein-based nanosystems within living organisms over millions of years. Among these are flagellin and pilin-based systems from bacteria, viral-based capsids, and eukaryotic microtubules and amyloids. While carbon nanotubes (CNTs), and protein/peptide-CNT composites, remain one of the most researched nanosystems due to their electrical and mechanical properties, there are many concerns regarding CNT toxicity and biodegradability. Therefore, proteins have emerged as useful biotemplates for nanomaterials due to their assembly under physiologically relevant conditions and ease of manipulation via protein engineering. This review aims to highlight some of the current research employing protein nanotubes (PNTs) for the development of molecular imaging biosensors, conducting wires for microelectronics, fuel cells, and drug delivery systems. The translational potential of PNTs is highlighted.

Protein Supramolecular Structures: From Self-Assembly to Nanovaccine Design

“…Such assemblies, apart from mimicking natural pathogens, present additional advantages for vaccine applications, including a small size, which enables localization to the lymph nodes and efficient uptake by APCs [6]. Protein nanorings are usually unilayered discs composed of 7 to 20 protein subunits and have diameters ranging from 8 to 20 nm [73,[89][90][91]. Nanorings are often the building blocks for larger protein assemblies, such as nanotubes.…”

“…Nanorings are often the building blocks for larger protein assemblies, such as nanotubes. Rings have similar supramolecular organization to those of helical viral capsids [89,90,92]. Such engineered assemblies presenting antigens on one face of the particle have shown an enhanced antibody response, potentially attributed to immune surface receptor clustering and activation, which constitutes a key aspect for the design of nanovaccines [6,93].…”

“…These nanocages are smaller than the majority of virus icosahedral capsids, such as adenoviruses and herpesviruses, whose capsid measures approximately 100 nm in diameter [109,110]. Nonetheless, cage nanoparticles are structurally similar to many plant viruses, such as the cowpea mosaic virus, and their size range (20 to 35 nm) is optimal for direct diffusion into the lymph vessels and uptake by APCs [6,89].…”

“…In contrast to fibrils, nanotubes are characterized by a hollow center cavity. The structure of these assemblies geometrically resembles the conformation of numerous pathogen-associated suprastructures, such as bacterial flagella and pili, helical viral capsids, and filaments from enterobacterial biofilms [6,89,111,112]. These elongated assemblies allow the stabilization and the repetitive display of antigens that can potentially activate T cell-independent immune responses, if the nanoscaffold is longer than 500 nm [6,80,81].…”

Synthesis and Characterization of Phenylalanine Nanotubes as Green pH‐Responsive Drug Nanocarriers

“…In addition, they can easily penetrate into the cellular membrane and have better flow dynamics than spherical nanoparticles [14] . Carbon, [15] silica, [16] lipids, [17] proteins, [18] peptides [19] and amino‐acids [20] are the most common materials for the synthesis of nanotube structures in drug delivery and biomedical applications, [21] among which, peptides and amino acids are the primary materials for the fabrication of nanotubes. These types of biomaterials have various advantages over carbon nanotubes; they are soluble in water and can be easily synthesized.…”