Back to Search
Start Over
Cooperative Binding of Substrate and Ions Drives Forward Cycling of the Human Creatine Transporter-1
- Source :
- Frontiers in Physiology, Vol 13 (2022)
- Publication Year :
- 2022
- Publisher :
- Frontiers Media S.A., 2022.
-
Abstract
- Creatine serves as an ATP buffer and is thus an integral component of cellular energy metabolism. Most cells maintain their creatine levels via uptake by the creatine transporter (CRT-1, SLC6A8). The activity of CRT-1, therefore, is a major determinant of cytosolic creatine concentrations. We determined the kinetics of CRT-1 in real time by relying on electrophysiological recordings of transport-associated currents. Our analysis revealed that CRT-1 harvested the concentration gradient of NaCl and the membrane potential but not the potassium gradient to achieve a very high concentrative power. We investigated the mechanistic basis for the ability of CRT-1 to maintain the forward cycling mode in spite of high intracellular concentrations of creatine: this is achieved by cooperative binding of substrate and co-substrate ions, which, under physiological ion conditions, results in a very pronounced (i.e. about 500-fold) drop in the affinity of creatine to the inward-facing state of CRT-1. Kinetic estimates were integrated into a mathematical model of the transport cycle of CRT-1, which faithfully reproduced all experimental data. We interrogated the kinetic model to examine the most plausible mechanistic basis of cooperativity: based on this systematic exploration, we conclude that destabilization of binary rather than ternary complexes is necessary for CRT-1 to maintain the observed cytosolic creatine concentrations. Our model also provides a plausible explanation why neurons, heart and skeletal muscle cells must express a creatine releasing transporter to achieve rapid equilibration of the intracellular creatine pool.
Details
- Language :
- English
- ISSN :
- 1664042X
- Volume :
- 13
- Database :
- Directory of Open Access Journals
- Journal :
- Frontiers in Physiology
- Publication Type :
- Academic Journal
- Accession number :
- edsdoj.ff70056a6ab347a1b8d283f6f512f111
- Document Type :
- article
- Full Text :
- https://doi.org/10.3389/fphys.2022.919439