Study Of Hβ2 Auxiliary Subunit Of BK Channels

hβ2 (KCNMB2) subunit is one of the auxiliary subunits of the large conductance voltage dependent and Ca2+activated potassium channel(BK or Maxi-K), which plays an important role in modulating the kinetics and the pharmacological properties of BK channels. This subunit is mainly expressed in chromaffin cells and brain. At present, much about the inactivation, Ca2+sensitivity and regulatory of gating properties of hβ2 subunit have been studied. However, the conformation of the transmembrane protein, especially the trafficking mechanism and the regulatory mechanism of gating are still unknown.In this study, by means of molecular cloning, and with the help of immunofluorescence and path-clamp techniques, we have determined the conformation and the trafficking mechanism of hβ2. Further more, we have studied the regulatory mechanism of gating of hβ2. The main results of this study are shown as follows.1. BK channels that assemble of hβ2 andαsubunit (mslo), the region flanking the 137 amino acid of the extracellular loop of hβ2 may be the only one domain that could be detected by immunofluorescence. This extracelluar region resides very closely to the outer pore of the channel. The discovery of this important region opens possibility for the further study of the trafficking and regulatory mechanism of this subunit.2. When coexpressed with mslo, hβ2 will transport to the membrane, while expressed alone hβ2 will reside in the ER (endoplasmic reticulum), revealing that hβ2 may contains a retention signal that prevent its membrane expression.3. We then have demonstrated that the retention signal is located at the NH2 terminus of hβ2. It is a motif consisting of five amino acids QKIRD. The motif is the core ofαhelix which is crucial for the retention process. Deletion or disruption of this core will decrease or get rid of the rentention signal.4. We have studied the extracellular loop of hβ2 and described the probably conformarion of the loop. The positive charged residues around position 137 of the extracellular loop may form a positive charged ring which makes BK channels possess the property of outward rectification.