Molecular determinants of inactivation and G protein modulation in the intracellular loop connecting domains I and II of the calcium channel alpha(1A) subunit
Molecular determinants of inactivation and G protein modulation in the intracellular loop connecting domains I and II of the calcium channel alpha(1A) subunit
复制标题
DOI：
10.1073/pnas.94.4.1512
复制
发表时间：
1997-02-18
影响因子：
11.1
通讯作者：
Catterall, WA
中科院分区：
文献类型：
--
作者：
Herlitze, S;Hockerman, GH;Catterall, WA
突触传递由G蛋白偶联受体调节，其激活释放调节突触前Ca2+通道的G蛋白β - γ亚基，序列基序QXXER被认为参与G蛋白β - γ亚基与靶蛋白（包括腺苷酸环化酶2）之间的相互作用。该基序存在于Ca2+通道α (1A)亚基的连接结构域I和II （L(I-II)）的胞内环中，由G蛋白调节，但不存在于α (1C)亚基中，α (1C)亚基不受调节。腺苷酸环化酶2或α (1A)中含有QXXER基序的肽段阻断G蛋白调节，但含有序列AXXAA的突变肽段不受调节，这表明α (1A)中含有QXXER的肽段可以竞争性地抑制G β γ调节。α (1A)的QQIER序列中的R与α (1C)中的R转化为E，减缓了通道失活，并将稳态失活的电压依赖性转移到更正的膜电位，α (1C)的QQLEE序列中的最终E转化为R对电压依赖性失活具有相反的影响，尽管变化不如α (1A)那么大。QQIER序列的突变α(1)QQIEE增强的G蛋白调制、和变异QQLEE如α(1 c)大大降低G蛋白调制和增加了G蛋白的逆转率的影响,这些结果表明,L的qx、主题(i ii)是一个重要的决定因素的压敏失活和G蛋白调制,在第三的位置,而氨基酸这个主题也出乎意料地大影响调制Gβγ。该基序与Ca2+通道β亚基结合的一致序列重叠表明，该区域的L（I-II）对Ca2+通道活性的三种不同调节影响很重要。
Synaptic transmission is regulated by G protein-coupled receptors whose activation releases G protein beta gamma subunits that modulate presynaptic Ca2+ channels, The sequence motif QXXER has been proposed to be involved in the interaction between G protein beta gamma subunits and target proteins including adenylyl cyclase 2. This motif is present in the intracellular loop connecting domains I and II (L(I-II)) of Ca2+ channel alpha(1A) subunits, which are modulated by G proteins, but not in alpha(1C) subunits, which are not modulated, Peptides containing the QXXER motif from adenylate cyclase 2 or from alpha(1A) block G protein modulation but a mutant peptide containing the sequence AXXAA does not, suggesting that the QXXER-containing peptide from alpha(1A) can competitively inhibit G beta gamma modulation, Conversion of the R in the QQIER sequence of alpha(1A) to E as in alpha(1C) slows channel inactivation and shifts the voltage dependence of steady-state inactivation to more positive membrane potentials, Conversion of the final E in the QQLEE sequence of alpha(1C) to R has opposite effects on voltage-dependent inactivation, although the changes are not as large as those for alpha(1A). Mutation of the QQIER sequence in alpha(1A) to QQIEE enhanced G protein modulation, and mutation to QQLEE as in alpha(1C) greatly reduced G protein modulation and increased the rate of reversal of G protein effects, These results indicate that the QXXER motif in L(I-II) is an important determinant of both voltage-dependent inactivation and G protein modulation, and that the amino acid in the third position of this motif has an unexpectedly large influence on modulation by G beta gamma. Overlap of this motif with the consensus sequence for binding of Ca2+ channel beta subunits suggests that this region of L(I-II) is important for three different modulatory influences on Ca2+ channel activity.