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The importance of occupancy rather than affinity of Ca V β subunits for the calcium channel I–II linker in relation to calcium channel function
Author(s) -
Butcher Adrian J.,
Leroy Jérôme,
Richards Mark W.,
Pratt Wendy S.,
Dolphin Annette C.
Publication year - 2006
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2006.109744
Subject(s) - linker , calcium , channel (broadcasting) , calcium channel , chemistry , relation (database) , n type calcium channel , biophysics , function (biology) , occupancy , t type calcium channel , biology , computer science , genetics , telecommunications , data mining , ecology , organic chemistry , operating system
The Ca V β subunits of voltage‐gated calcium channels regulate the trafficking and biophysical properties of these channels. We have taken advantage of mutations in the tyrosine residue within the alpha interaction domain (AID) in the I–II linker of Ca V 2.2 which reduce, but do not abolish, the binding of β1b to the AID of Ca V 2.2. We have found that the mutation Y388S decreased the affinity of Ca V β1b binding to the Ca V 2.2 I–II linker from 14 to 329 n m . However, the Y388S mutation had no effect on current density and cell surface expression of Ca V 2.2/α2δ‐2/β1b channels expressed in human embryonic kidney tsA‐201 cells, when equivalent proportions of cDNA were used. Furthermore, despite the 24‐fold reduced affinity of Ca V β1b for the Y388S I–II linker of Ca V 2.2, all the key features of modulation as well as trafficking by Ca V β subunits remained intact. This is in contrast to the much more marked effect of the W391A mutation, which abolished interaction with the Ca V 2.2 I–II linker, and very markedly affected the trafficking of the channels. However, using the Xenopus oocyte expression system, where expression levels can be accurately titrated, when Ca V β1b cDNA was diluted 50‐fold, all evidence of interaction with Ca V 2.2 Y388S was lost, although wild‐type Ca V 2.2 was still normally modulated by the reduced concentration of β1b. These results indicate that high affinity interaction with the α1 subunit is not necessary for any of the modulatory effects of Ca V β subunits, but occupancy of the interaction site is important, and this will occur, despite the reduced affinity, if the Ca V β subunit is present in sufficient excess.