Four-turn alpha-helical segment prevents surface expression of the auxiliary hbeta2 subunit of BK-type channel.
Large conductance, voltage- and Ca2+-activated K+ (BK) channels encoded by the mslo alpha and beta2 subunits exist abundantly in rat chromaffin cells, pancreatic beta cells, and DRG neurons. The extracellular loop of hbeta2 acting as the channel regulator influences the rectification and toxin sensitivity of BK channels, and the inactivation domain at its N terminus induces rapid inactivation. However, the regulatory mechanism, especially the trafficking mechanism of hbeta2, is still unknown. With the help of immunofluorescence and patch clamp techniques, we determine that the hbeta2 subunit alone resides in the endoplasmic reticulum, suggesting that trafficking mechanism of hbeta2 differs from that of hbeta1 opposite to what we predicted previously. We further demonstrate that a four-turn alpha helical segment at the N terminus of hbeta2 prevents the surface expression of hbeta2, that is, the helical segment itself is a retention signal. Using the c-Myc epitope-tagged extracellular loop of hbeta2, we reveal that the most accessible site by antibody is located at the middle of the extracellular loop, which might provide clues to understand how the auxiliary beta subunits regulates the toxin sensitivity and the rectification of BK-type channels.
Lv
Caixia
C
Key Laboratory of Molecular Biophysics (Huazhong University of Science and Technology), Ministry of Education, Wuhan, Hubei, China.
Chen
Maorong
M
Gan
Geliang
G
Wang
Lifen
L
Xu
Tao
T
Ding
Jiuping
J
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D018408:Patch-Clamp Techniques; D017433:Protein Structure, Secondary; D021122:Protein Subunits; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D051036:Large-Conductance Calcium-Activated Potassium Channels; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins