Osmoregulation: Homeostasis is vital for bacteria
Structural investigation by cryo-electron microscopy on a bacterial potassium ion-proton symporter
A research group led by Janet Vonck of the Max Planck Institute of Biophysics and Inga Hänelt of the Goethe University Frankfurt am Main examined the K+/H+ importer KimA, which belongs to the KUP family.
A balanced potassium concentration is essential for the survival of all organisms from bacteria to humans. For bacteria, controlled potassium uptake is often difficult because they are continuously exposed to strong fluctuations of environmental conditions. The potassium ions can only be specifically taken up by specific membrane transport proteins; the cell membrane is impermeable to potassium ions.
With the help of cryo-electron microscopy the structure of KimA was determined up to a resolution of 3.7 Å, the first structure of a KUP (K+ uptake permease) family member. Of particular interest is the region that can bind potassium ions. Here are conserved amino acids within the KUP family, which can bind K+ and H+. This was shown by point mutations.
Three potassium ion binding sites were identified in the transmembrane region of the protein. In the present structure the KimA homodimer has an inwardly closed, trans-inhibited conformation.
The cryo-EM map and the model were deposited in the wwPDB with accession codes EMD-10092 and 6S3K, respectively.