Table 2:

List of major structural components of EVs have been listed (we have used a standardized table developed to describe viral pathogens)

Structure	Available information
Lipid envelope	EVs are small, spherical viruses made up of an RNA genome surrounded by a protein shell.These viruses lack a “membrane.”87
Glycoproteins	Proteins such as A9 and 3A are important; interact with host secretory carrier membrane protein 3 and participate in viral replication.87
Receptor-binding motifs	The arginine–glycine–aspartic acid (RGD) motif found in the VP1 capsid protein of CV-A9 has a role in cell entry. This motif binds integrins to promote entry into the cells.88
Envelope protein E	Either not expressed or relevance unclear in fetal/infantile disease.
Membrane protein	Either not expressed or relevance unclear in fetal/infantile disease.
MHC or HLA Proteins	Either not expressed or relevance unclear in fetal/infantile disease.
Spike protein	Either not expressed or relevance unclear in fetal/infantile disease.
Surface tubules	Lipid droplets (LDs) are transported to lysosomes by autophagy. Lipases are recruited to the LD surface for sequential hydrolysis of TGs stored within LDs. After enterovirus infection, TGs within LDs transformed into fatty acids.89
Palisade layer	Either not expressed or relevance unclear in fetal/infantile disease.
Viral tegument	Either not expressed or relevance unclear in fetal/infantile disease.
Lateral bodies	Either not expressed or relevance unclear in fetal/infantile disease.
Capsid	EVs are small (approximately 27 nm), non-enveloped virions with an icosahedral capsid with 60 subunits, each formed from four proteins (VP1 to VP4).9
Capsomeres	Viral polyprotein domains (from P1 to P3) are cleaved into 3–4 domains each; P1 is liberated from the polyprotein by 2A protein. Amino acids in the loops that extend from the β-barrel domain of VP1, VP2, and VP3 give the EVs their distinct antigenicity.
Core membrane	Either not expressed or relevance unclear in fetal/infantile disease.9
Protein core	Details on genome-associated polyprotein are described below.
Core fibrils	Either not expressed or relevance unclear in fetal/infantile disease.
Matrix	Virions penetrating the cell surface get uncoated and the viral genome functions as mRNA for the viral polyprotein.90
Enzymes	Details scant. Alter the expression of host enzymes.91
RNA elements	Enteroviral 3’ non-translated regions (3’NTR) are comprised of two (X and Y) hairpin structures.92
Nucleus	Either not expressed or relevance unclear in fetal/infantile disease.
Nucleosome	Either not expressed or relevance unclear in fetal/infantile disease.
DNA	No DNA genome exists
RNA	The enteroviral genome (7.5-8 kb) is flanked by a 5’-UTR that is composed of an RNA cloverleaf structure and an internal ribosomal entry site (IRES).5,9
Genome-associated polyprotein	A single polyprotein is cleaved by the host and viral protease into 4 capsid VP proteins and 7 non-structural proteins. The capsid protein VP1 varies and confers antigenic properties.93
RNA polymerase	The RNA-dependent RNA polymerase (RdRP), known as 3D protein, functions as a replica for viral RNA synthesis in infected cells.94
Reverse transcriptase	Either not expressed or relevance unclear in fetal/infantile disease.
Head	Either not expressed or relevance unclear in fetal/infantile disease.
Base plate	Either not expressed or relevance unclear in fetal/infantile disease.
Integrase	Either not expressed or relevance unclear in fetal/infantile disease.
Tail	Either not expressed or relevance unclear in fetal/infantile disease.
Tail fiber	Either not expressed or relevance unclear in fetal/infantile disease.
Neck	Either not expressed or relevance unclear in fetal/infantile disease.

HLA, human leukocyte antigens; MHC, major histocompatibility complex; TGs, triglycerides