返回Google圖書搜尋

The Effects of Post-translational Modifications of Voltage-dependent Calcium Channel [MARC+BB] Subunits on Channel Targeting and Function

出版	Northwestern University, 1998
URL	http://books.google.com.hk/books?id=XiAdAQAAMAAJ&hl=&source=gbs_api

註釋Voltage-dependent calcium channels (VDCCs) remain among the most extensively characterized channels from an electrophysiological standpoint, yet relatively little is known about the biochemical properties of these proteins due to their rarity in native tissues. While considerable data has been accumulated on the biophysical effects of VDCC $\beta$ subunits on Ca$\sp{2+}$ channel currents, much remains to be learned about the biochemical events involved in the regulation of channels by these proteins. To further address the role of $\beta$ subunits in channel regulation and maturation, we employed a multifaceted approach utilizing biochemistry, molecular biology, pharmacology, immunohistochemistry and electrophysiology to analyze the properties of $\beta$ subunits and their functional modulation of VDCC $\alpha\sb1$ subunits. Studies of the cardiac L-type channel $\rm\alpha\sb{1C}$ and $\rm\beta\sb{2a}$ subunits heterologously expressed in human embryonic kidney (HEK) cells revealed that co-expression of the $\beta$ subunit was necessary for the formation and targeting of functional channels to the cell surface. Unexpectedly, the $\rm\beta\sb{2a}$ subunit localized to the plasma membrane in the absence of the $\rm\alpha\sb{1C}$ subunit, despite having a highly hydrophilic sequence with no predicted transmembrane-spanning regions. Studies demonstrated that the $\rm\beta\sb{2a}$ subunit was palmitoylated at sites located in the N-terminus which were unique to the $\rm\beta\sb{2a}$ isoform. By contrast, three other known $\beta$ subunit isoforms were not palmitoylated, suggesting that expression of a channel with the $\rm\beta\sb{2a}$ isoform could allow selective regulation through palmitoylation. The loss of palmitoylation did not affect the formation and targeting of channels, but did affect the modulation of channel currents. Additionally, palmitoylation appeared to be critical for the plasma membrane localization observed with the uncomplexed $\rm\beta\sb{2a}$ subunit. Mutations in other domains of the $\rm\beta\sb{2a}$ subunit also appeared to affect palmitoylation and subcellular localization, potentially through the disruption of interactions critical for protein targeting and/or recognition by enzymes involved in palmitoylation. Future studies may determine the role of palmitoylation in the regulation of VDCCs in native cells, as well as the mechanisms by which palmitoylation may be regulated.