ACE2 and COVID-19: Two of these heterodimer functional units behave within the physical structure of an [ACE2:B0AT1]2 dimer-of-heterodimers 4-mer complex, with PDB ID: 6M18 atomic coordinates measured by Yan et al.1 Notably, these data are consistent with our prior molecular docking modeling55,56 and gut–lung axis studies,33,34,81 and prescient antecedent literature review17 that putatively implicated the B0AT1 subunit as a major player with ACE2 in SARS-CoV-2 gastrointestinal tropism in COVID-19.