Locating an extracellular K -dependent interaction site that modulates betaine-binding of the Na -coupled betaine symporter BetP

摘要

BetP is a transport protein found in the inner cellular membrane of the bacterium Corynebacterium glutamicum. Specifically, BetP transports one zwitterionic betaine-an important compound that promotes protein folding and protects the cell against osmotic and cold stresses-together with two sodium ions in the same direction across the cell membrane. BetP regulates the rate of betaine transport according to the concentration of the surrounding solution via a sophisticated network of interactions within and between the individual protomers, of the BetP trimer (1). Based on a wealth of functional and structural data, BetP is a paradigm for regulated transporters (2). Under conditions in which the solute concentration is normal (isotonic) or low (hypotonic), BetP shows nearly no activity.