Structural Biology of Membrane Transport Proteins
Understanding the complexity of life requires that scientists have a deeper understanding of how molecules in cells function and interact. Integral membrane proteins play key roles in cell transport of ions and substrates, signaling and receptor function. It is estimated that that approximately 25% of the human genome encodes membrane proteins. They are important targets for pharma as approximately 60% of drugs on the market target membrane proteins. Mutations in these proteins are associated with disorders such as diabetes, obesity, cancer, obesity, Alzheimer’s and Parkinson’s disease. Structural biology has played a key role at the atomic level in understanding structure function relationships of membrane proteins. Techniques such as x-ray crystallography, cryo-EM, NMR and neutron diffraction have played important roles. The importance of SLC4 bicarbonate/carbonate transporters in human biology is highlighted by the diseases associated with their functional loss including blindness, short stature, abnormal cognitive function, cerebral calcification, metabolic acidosis, anemia and hearing abnormalities. By combining cryo-EM structural analysis with functional mutagenesis studies, we have reported for the first time the near-atomic structures of the electrogenic NBCe1, an electrogenic Na+-CO32- cotransporter and NDCBE, the Na+-CO32-/Cl- exchanger.
Functional Properties of SLC4 Transporters
SLC4 transporters are a family 10 membrane proteins most of whom transport bicarbonate or carbonate coupled to Na+ and/or Cl- in many cell types. These proteins play key roles in the brain, heart, kidney, eye and ear and are involved in the maintenance of systemic acid-base chemistry and in maintaining the normal ionic milieu of various cell types. Our laboratory has discovered and cloned several SLC4 transporters and has characterized their functional properties using microscopic fluorescent pH and patch clamp methodologies. One of the transporters, SLC4A11 which is involved in ocular CHED disease has been a recent focus of the lab where we have published evidence that this transporter is unique among SLC4 proteins in that it transports NH3 and a H+. The role of SLC4A11 in the kidney is not well understood. We demonstrated the selective expression of SLC4A11 in the nephron upper descending thin limbs (DTLs) (which are aquaporin (AQP1)‐positive) in the outer medulla and inner medulla with little or no expression in the lower DTLs (which are AQP‐1‐null). SLC4A11 also colocalized with AQP1 and the urea transporter UT‐B in the mouse descending vasa recta, but was absent in mouse and rat ascending vasa recta. Mouse, but not rat, outer medullary collecting duct cells also labeled for SLC4A11. We hypothesized that in the inner stripe of the outer medulla, SLC4A11 plays a role in the countercurrent transport of ammonia absorbed from the outer medullary thick ascending limb and secreted into the long‐looped DTLs.
Development of an Artificial Kidney
Current clinical approaches to treat patients with end stage renal disease (ESRD) include hemodialysis, peritoneal dialysis, and renal transplantation. We have developed a novel dialysis-free and waterless artificial kidney technology that has the potential to mimic the filtration properties of the renal glomerulus and the ion/water transport processes in the nephron. Importantly, the device does not utilize external water/dialysate or living cells. This waterless technology creates more than a replacement for dialysis, it allows increased freedom for patients. Since the technology does not utilize a dialysate, the portable device we are developing is self-enclosed and operated without having to worry about where to source or dispose of dialysate and water. Additionally, for providers, our waterless technology will completely eliminate the massive water infrastructure and associated costs currently needed to perform standard dialysis treatments. The technologic advances and approaches employed in this proposal can be potentially utilized in various configurations that include standalone, portable and implantable artificial kidney devices to treat patients with compromised kidney function. The device couples for the first time newly designed multiple mesh activated wafer electrodeionization (AWEDI) technology for ion transport that responds functionally using ion sensors to changes in blood chemistry, with pressure driven low-fouling ultrafiltration, nanofiltration and reverse osmosis modules specifically developed or selected for this project. The technology is a paradigm shift in the field of renal replacement therapy that compares with the introduction of dialysis as a therapeutic modality over 70 years ago. The novel technology we have developed in our waterless portable artificial kidney device will potentially in the future be used to create for the first time a completely implantable artificial kidney that simulates the filtration and ion transport properties of the native kidney.
Artificial Intelligence and Machine Learning
Advancements in computing power and software has made it possible for artificial intelligence (AI) and its subfields of machine learning, reinforcement learning, and deep learning to analyze large amounts of medical data from the EMR. We are utilizing AI in the context of optimization decision-making in the context of dialysis; specifically, in the technique called CRRT. This dialytic approach is utilized in patients with suboptimal hemodynamics and is associated with a high mortality. There is currently insufficient data and clinical guidelines to determine which patients should be started on CRRT and which patients should have CRRT stopped. We are analyzing all appropriate patients who have received CRRT where the EMR is available. In collaborations with computer scientists, we are hoping to develop algorithms that can be used clinically in their decision making.
