B0AT1 Amino Acid Transporter Complexed With SARS-CoV-2 Receptor ACE2 Forms a Heterodimer Functional Unit: In Situ Conformation Using Radiation Inactivation Analysis

Bruce R Stevens; J Clive Ellory; Robert L Preston

doi:10.1093/function/zqab027

B⁰AT1 Amino Acid Transporter Complexed With SARS-CoV-2 Receptor ACE2 Forms a Heterodimer Functional Unit: In Situ Conformation Using Radiation Inactivation Analysis

Function (Oxf). 2021 May 13;2(4):zqab027. doi: 10.1093/function/zqab027. eCollection 2021.

Authors

Bruce R Stevens¹, J Clive Ellory², Robert L Preston³

Affiliations

¹ Department of Physiology and Functional Genomics, University of Florida College of Medicine, Gainesville, FL, 32610, USA.
² Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, OX1 3PT, UK.
³ School of Biological Sciences, Illinois State University, Normal, IL, 61790, USA.

Abstract

The SARS-CoV-2 receptor, angiotensin-converting enzyme-2 (ACE2), is expressed at levels of greatest magnitude in the small intestine as compared with all other human tissues. Enterocyte ACE2 is coexpressed as the apical membrane trafficking partner obligatory for expression and activity of the B⁰AT1 sodium-dependent neutral amino acid transporter. These components are assembled as an [ACE2:B⁰AT1]₂ dimer-of-heterodimers quaternary complex that putatively steers SARS-CoV-2 tropism in the gastrointestinal (GI) tract. GI clinical symptomology is reported in about half of COVID-19 patients, and can be accompanied by gut shedding of virion particles. We hypothesized that within this 4-mer structural complex, each [ACE2:B⁰AT1] heterodimer pair constitutes a physiological "functional unit." This was confirmed experimentally by employing purified lyophilized enterocyte brush border membrane vesicles exposed to increasing doses of high-energy electron radiation from a 16 MeV linear accelerator. Based on radiation target theory, the results indicated the presence of Na⁺-dependent neutral amino acid influx transport activity functional unit with target size molecular weight 183.7 ± 16.8 kDa in situ in intact apical membranes. Each thermodynamically stabilized [ACE2:B⁰AT1] heterodimer functional unit manifests the transport activity within the whole ∼345 kDa [ACE2:B⁰AT1]₂ dimer-of-heterodimers quaternary structural complex. The results are consistent with our prior molecular docking modeling and gut-lung axis approaches to understanding COVID-19. These findings advance understanding the physiology of B⁰AT1 interaction with ACE2 in the gut, and thereby contribute to translational developments designed to treat or mitigate COVID-19 variant outbreaks and/or GI symptom persistence in long-haul postacute sequelae of SARS-CoV-2.

Keywords: 6M17; ACE2; B0AT1; intestine; membrane; neutral amino acid transport; radiation inactivation; sodium-dependent transport; transporter.

Publication types

Comment

MeSH terms

Amino Acid Transport Systems
Amino Acid Transport Systems, Neutral* / metabolism
Amino Acids, Neutral*
Angiotensin-Converting Enzyme 2 / metabolism
COVID-19*
Humans
Molecular Docking Simulation
Peptidyl-Dipeptidase A / metabolism
SARS-CoV-2 / metabolism

Substances

Angiotensin-Converting Enzyme 2
Peptidyl-Dipeptidase A
Amino Acid Transport Systems, Neutral
Amino Acid Transport Systems
Amino Acids, Neutral

Supplementary concepts

SARS-CoV-2 variants