Table 1.

Function, structure, and production of the most commonly used protein-based nanoparticles (PNPs).

PNP		Native Organism	Biological Function	Geometry	Number of Subunits	Size (Diameter)	Heterologous Production	Ref.
Virus-like particles (VLPs)	CCMV 1	Cowpea chlorotic mottle virus capsid protein	Plant virus	Icosahedral	182	28 nm	Plants; yeast; Escherichia coli; Pseudomonas fluorescens	[11,28,29,30]
	CPMV 2	Cowpea mosaic virus capsid protein	Plant virus	Pseudo icosahedral	120 Large (L) and 120 Small (S)	28 nm	Insect cells; plants	[31,32]
	HBc 3	Hepatitis B virus capsid protein	Human virus	Icosahedral	180 or 240	30 nm or 34 nm	Mammalian cells; insect cells; plants; yeast; E. coli; cell-free	[33,34,35,36,37,38]
	MS2	Enterobacteriaceae	Bacteriophage	Icosahedral	180	26 nm	Yeast; E. coli; cell-free	[39,40,41]
	P22	Salmonella typhimurium	Bacteriophage	Icosahedral	420	60 nm	E. coli	[42]
	Qβ	E. coli	Bacteriophage	Icosahedral	180	28 nm	Yeast; E. coli; cell-free	[43,44,45]
Non-viral PNPs	Dps 4 (mini-ferritin)	Archaea; Bacteria (e.g., Listeria innocua)	Involved in oxidative and starvation responses	Tetrahedral	12	9 nm	E. coli	[46,47]
	E2	Bacillus stearothermophilus	Core of the pyruvate dehydrogenase multienzyme complex	Dodecahedral	60	24 nm	E. coli	[48]
	Encapsulin	Archaea; Bacteria	Involved in oxidative stress response	Icosahedral	60 or 180	20–40 nm	Mammalian cells; yeast; E. coli	[49,50,51,52]
	Ferritin (maxi-ferritin)	Archaea; Bacteria; Eukarya	Iron storage	Octahedral	24	12 nm	Mammalian cells; insect cells; yeast; E. coli	[53,54,55,56,57,58]
	Hsp 5	Archaea; Bacteria; Eukarya (e.g., Methanococcus jannaschii)	Chaperone	Octahedral	24	12 nm	E. coli	[59,60]
	Lumazine synthase	Archaea; Bacteria; Eukarya (e.g., Aquifex aeolicus)	Mediates the biosynthesis of riboflavin	Icosahedral	60	15.4 nm	E. coli	[61,62]
	Vault protein	Eukarya	Involved in signaling and immune responses	39-fold dihedral	78 Major vault protein	Diameter: 40 nm Length: 67 nm	Insect cells; cell-free	[63,64,65,66]

¹ Cowpea chlorotic mottle virus, ² Cowpea mosaic virus, ³ Hepatitis virus, ⁴ DNA-binding proteins from starved cells, ⁵ Heat shock proteins.