The activity of potassium(K+) channels critically depends on their density on the cell surface membrane,which is regulated by dynamic protein–protein in teractions that often involve distinct trafficking signals on the cargo proteins.In this paper we explored the possibility of utilizing the Saccharomyces cerevisiae strain B31 for identification of the signal motifs that regulate surface expression of membrane proteins and for studying structure–function relationships of K+ channels. B31 cells lack the K+efflux system and were reported to show overloaded K+-mediated growth inhibition in high K+ media
upon heterologous expression of a mammalian inwardly rectifying K+ channel(Kir2.1).We show that while the expression of wild-type Kir2.1 channel inhibits the growth of B31 cells in high K+ media,the human disease causing mutations of Kir2.1 that abolish K+ conduction (V302M) or surface trafficking (314/315) fully restores the growth.The expression of two-pore-domain K+channel KCNK3 or KCNK9 also inhibited the growth of B31 in high k+media while C-terminal mutations that reducetheir14-3-3
protein-dependentcellsurfacetraffickingrestoredthegrowthofB31.Finally,theexpressionofKir2.1
channelsthatwereC-terminallyfusedwithknownsequencemotifsincluding ERretention/retrieval
signalsandanendocytosissignalallowedthegrowthofB31inhighK
+
media.TheseresultsdemonstratethepotentialofB31yeaststrainasauniquebiologicaltooltoscreentherandompeptidelibraries
fornovelsequencesignalsthatdown-regulatesurfaceexpressionofmembraneproteins,aswellasto
systematicallyidentifythestructuraldeterminantsforcellsurfacetraffickingand/orionconductance
ofK
+
channels.