Combination of hydrophobicity and codon usage bias determines sorting of model K channel protein to either mitochondria or endoplasmic reticulum.

When the K channel-like protein Kesv from Ectocarpus siliculosus virus 1 is heterologously expressed in mammalian cells, it is sorted to the mitochondria. This targeting can be redirected to the endoplasmic reticulum (ER) by altering the codon usage in distinct regions of the gene or by inserting a triplet of hydrophobic amino acids (AAs) into the protein's C-terminal transmembrane domain (ct-TMD). Systematic variations in the flavor of the inserted AAs and/or its codon usage show that a positive charge in the inserted AA triplet alone serves as strong signal for mitochondria sorting.

Codon Bias Can Determine Sorting of a Potassium Channel Protein.

Due to the redundancy of the genetic code most amino acids are encoded by multiple synonymous codons. It has been proposed that a biased frequency of synonymous codons can affect the function of proteins by modulating distinct steps in transcription, translation and folding. Here, we use two similar prototype K channels as model systems to examine whether codon choice has an impact on protein sorting.

Light-Regulated Transcription of a Mitochondrial-Targeted K Channel.

The inner membranes of mitochondria contain several types of K channels, which modulate the membrane potential of the organelle and contribute in this way to cytoprotection and the regulation of cell death. To better study the causal relationship between K channel activity and physiological changes, we developed an optogenetic platform for a light-triggered modulation of K conductance in mitochondria. By using the light-sensitive interaction between cryptochrome 2 and the regulatory protein CIB1, we can trigger the transcription of a small and highly selective K channel, which is in mammalian cells targeted into the inner membrane of mitochondria.