Functional characterization of two RAB27A missense mutations found in Griscelli syndrome type 2
Functional characterization of two RAB27A missense mutations found in Griscelli syndrome type 2
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DOI：
10.1111/j.1755-148x.2010.00705.x
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发表时间：
2010-06-01
影响因子：
4.3
通讯作者：
Parvaneh, Nima
中科院分区：
文献类型：
--
作者：
Ohbayashi, Norihiko;Mamishi, Setareh;Parvaneh, Nima
人类Griscelli综合征2型（GS-2）的特征是部分白化病和由于RAB 27 A突变导致的严重免疫紊乱。在黑素细胞中，Rab 27 A与特异性效应子Slac 2-a/亲黑素蛋白和肌球蛋白Va形成三方复合物，并且该复合物调节黑素体转运。在这里，我们报告了一种新的纯合错义突变Rab 27 A，即K22 R，在波斯GS-2患者和K22 R突变和先前报道的I44 T突变对蛋白质功能的影响的分析结果。这两种突变都完全消除了Slac 2-a/亲黑素蛋白结合活性，但它们不同地影响Rab 27 A的生物化学性质。Rab 27 A（K22 R）突变体缺乏GTP结合能力，并且在黑素细胞中表现出胞质定位。相比之下，Rab 27 A的内在GT3活性和黑素体定位均不受I44 T突变的影响，但Rab 27 A（I44 T）突变体不能募集Slac 2-a/黑素蛋白。有趣的是，这两个突变不同地影响与其他Rab 27 A效应子Slp 2-a、Slp 4-a/颗粒蛋白-a和Munc 13 -4的结合。Rab 27 A（K22 R）突变体通常结合Munc 13 -4，但不结合Slp 2-a或Slp 4-a，而Rab 27 A（I44 T）突变体显示降低的与Slp 2-a和Munc 13 -4的结合活性，但通常结合Slp 4-a。
P>Human Griscelli syndrome type 2 (GS-2) is characterized by partial albinism and a severe immunologic disorder as a result of RAB27A mutations. In melanocytes, Rab27A forms a tripartite complex with a specific effector Slac2-a/melanophilin and myosin Va, and the complex regulates melanosome transport. Here, we report a novel homozygous missense mutation of Rab27A, i.e. K22R, in a Persian GS-2 patient and the results of analysis of the impact of the K22R mutation and the previously reported I44T mutation on protein function. Both mutations completely abolish Slac2-a/melanophilin binding activity but they affect the biochemical properties of Rab27A differently. The Rab27A(K22R) mutant lacks the GTP binding ability and exhibits cytosolic localization in melanocytes. By contrast, neither intrinsic GTPase activity nor melanosomal localization of Rab27A is affected by the I44T mutation, but the Rab27A(I44T) mutant is unable to recruit Slac2-a/melanophilin. Interestingly, the two mutations differently affect binding to other Rab27A effectors, Slp2-a, Slp4-a/granuphilin-a, and Munc13-4. The Rab27A(K22R) mutant normally binds Munc13-4, but not Slp2-a or Slp4-a, whereas the Rab27A(I44T) mutant shows reduced binding activity to Slp2-a and Munc13-4 but normally binds Slp4-a.