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Stevens, B. R.

Publications and source records attributed to Stevens, B. R..

2 recordsLinked to original sources
bioRxiv2020

TMPRSS2 and ADAM17 interactions with ACE2 complexed with SARS-CoV-2 and B0AT1 putatively in intestine, cardiomyocytes, and kidney

COVID-19 outcomes reflect organ-specific interplay of SARS-CoV-2 and its receptor, ACE2, with TMPRSS2 and ADAM17. Confirmed active tropism of SARS-CoV-2 in epithelial cells of intestine and kidney proximal tubule, and in aging cardiomyocytes, capriciously manifests extra-pulmonary organ-related clinical symptoms in about half of COVID-19 patients, occurring by poorly understood mechanisms. We approached this knowledge gap by recognizing a clue that these three particular cell types share a common denominator kindred of uniquely expressing the SLC6A19 neutral amino acid transporter B0AT1 protein (alternatively called NBB, B, B0) serving glutamine and tryptophan uptake. B0AT1 is a cellular trafficking chaperone partner of ACE2, shown by cryo-EM to form a thermodynamically-favored stabilized 2ACE2:2B0AT1 dimer-of-heterodimers. The gut is the bodys site of greatest magnitude expression depot of both ACE2 and B0AT1. This starkly contrasts with pulmonary pneumocyte expression of monomeric ACE2 with conspicuously undetectable B0AT1. We hypothesized that B0AT1 steers the organ-related interplay amongst ACE2, TMPRSS2, ADAM17, and SARS-CoV-2 RBD. The present study employed molecular docking modeling that indicated active site catalytic pocket residues of TMPRSS2 and ADAM17 each formed bonds [≤] 2 A with monomer ACE2 specific residues within a span R652-D713 involved in cleaving sACE2 soluble ectodomain release. These bonds are consistent with competitive binding interactions of experimental anti-SARS-CoV-2 drug small molecules including Camostat and Nafamostat. Without B0AT1, ACE2 residues K657 and N699 dominated docking bonding with TMPRSS2 or ADAM17 active sites, with ACE2 R710 and R709 contributing electrostatic attractions, but notably ACE2 S708 never closer than 16-44 A. However, in the dimer-of-heterodimers arrangement all ACE2 neck region residues were limited to TMPRSS2 or ADAM17 approaches 35 A, with the interference directly attributed to the presence of a neighboring B0AT1 subunit complexed to the partnering ACE2 subunit of 2ACE2:2B0AT1; ADAM17 failed to dock by bumping its active site pocket oriented dysfunctionally outwardly facing 1800 away. Results were the same whether the dimer-of-heterodimers was in either the "closed" or "open" conformation, or whether or not SARS-CoV-2 RBD was complexed to ACE2. The results implicate B0AT1-and in particular the 2ACE2:2B0AT1 complex-as a maJor player in the landscape of COVID-19 pathophysiology engaging TMPRSS2 and ADAM17, consistent with experimental evidence in the literature and in clinical reports. These findings provide a gateway to understanding the roles of B0AT1 relating to COVID-19 manifestations putatively assigned to intestinal and renal epithelial cells and cardiomyocytes, with underpinnings useful for considerations in public hygiene policy and drug development.

biochemistry↗
bioRxiv2020

Amino acid transporter B0AT1 influence on ADAM17 interactions with SARS-CoV-2 receptor ACE2 putatively expressed in intestine, kidney, and cardiomyocytes

SARS-CoV-2 exhibits significant experimental and clinical gastrointestinal, renal, and cardiac muscle tropisms responsible for local tissue-specific and systemic pathophysiology capriciously occurring in about half of COVID-19 patients. The underlying COVID-19 mechanisms engaged by these extra-pulmonary organ systems are largely unknown. We approached this knowledge gap by recognizing that neutral amino acid transporter B0AT1 (alternately called NBB, B, B0 in the literature) is a common denominator expressed nearly exclusively by three particular cell types: intestinal epithelia, renal proximal tubule epithelium, and cardiomyocytes. B0AT1 provides uptake of glutamine and tryptophan. The gut is the main depot expressing over 90% of the bodys entire pool of SARS-CoV-2 receptor angiotensin converting enzyme-2 (ACE2) and B0AT1. Recent cryo-EM studies established that ACE2 forms a thermodynamically favored dimer-of-heterodimers complex with B0AT1 assembled in the form of a dimer of two ACE2:B0AT1 heterodimers anchored in plasma membranes. Prior epithelial cell studies demonstrated ACE2 chaperone trafficking of B0AT1. This contrasts with monomeric expression of ACE2 in lung pneumocytes, in which B0AT1 is undetectable. The cell types in question also express a disintegrin and metalloproteinase-17 (ADAM17) known to cleave and shed the ectodomain of monomeric ACE2 from the cell surface, thereby relinquishing protection against unchecked renin-angiotensin-system (RAS) events of COVID-19. The present study employed molecular docking modeling to examine the interplaying assemblage of ACE2, ADAM17 and B0AT1. We report that in the monomer form of ACE2, neck region residues R652-N718 provide unimpeded access to ADAM17 active site pocket, but notably R708 and S709 remained >10-15 [A] distant. In contrast, interference of ADAM17 docking to ACE2 in a dimer-of-heterodimers arrangement was directly correlated with the presence of a neighboring B0AT1 subunit complexed to the partnering ACE2 subunit of the 2ACE2:2B0AT1] dimer of heterodimers, representing the expression pattern putatively exclusive to intestinal, renal and cardiomyocyte cell types. The monomer and dimer-of-heterodimers docking models were not influenced by the presence of SARS-CoV-2 receptor binding domain (RBD) complexed to ACE2. The results collectively provide the underpinnings for understanding the role of B0AT1 involvement in COVID-19 and the role of ADAM17 steering ACE2 events in intestinal and renal epithelial cells and cardiomyocytes, with implications useful for consideration in pandemic public hygiene policy and drug development.

biochemistry↗