Carbon dioxide transport across membranes
Abstract
Carbon dioxide (CO2) movement across cellular membranes is passive and governed by Fick's law of diffusion. Until recently, we believed that gases cross biological membranes exclusively by dissolving in and then diffusing through membrane lipid. However, the observation that some membranes are CO2impermeable led to the discovery of a gas molecule moving through a channel; namely, CO2diffusion through aquaporin-1 (AQP1). Later work demonstrated CO2diffusion through rhesus (Rh) proteins and NH3diffusion through both AQPs and Rh proteins. The tetrameric AQPs exhibit differential selectivity for CO2versus NH3versus H2O, reflecting physico-chemical differences among the small molecules as well as among the hydrophilic monomeric pores and hydrophobic central pores of various AQPs. Preliminary work suggests that NH3moves through the monomeric pores of AQP1, whereas CO2moves through both monomeric and central pores. Initial work on AQP5 indicates that it is possible to create a metal-binding site on the central pore's extracellular face, thereby blocking CO2movement. The trimeric Rh proteins have monomers with hydrophilic pores surrounding a hydrophobic central pore. Preliminary work on the bacterial Rh homologue AmtB suggests that gas can diffuse through the central pore and three sets of interfacial clefts between monomers. Finally, initial work indicates that CO2diffuses through the electrogenic Na/HCO3cotransporter NBCe1. At least in some cells, CO2-permeable proteins could provide important pathways for transmembrane CO2movements. Such pathways could be amenable to cellular regulation and could become valuable drug targets.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Feb 12, 2021
- Source ID
- 10.1098/rsfs.2020.0090
Entities
People
- Ardeschir Vahedi-faridi
- Brian S. Zeise
- Dengke Wang
- Emad Tajkhorshid
- Eric Shinn
- Fraser J Moss
- Hyea J. Hwang
- Marie Michenkova
- Matthew C. Blosser
- Noah Malmstadt
- Pan Zhao
- Rossana Occhipinti
- Sara Taki
- Soumyo Sen
- Thomas Kowatz
- Walter Boron
- Xue Qin
Organizations
- Case Western Reserve University
- National Institute of General Medical Sciences
- United States Department of Defense
- University of Illinois Urbana–Champaign
- University of Southern California