IQGAP1, a Rac- and Cdc42-binding protein, directly binds and cross-links microfilaments.
IQGAP1, a Rac- and Cdc42-binding protein, directly binds and cross-links microfilaments.
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DOI：
10.1083/jcb.137.7.1555
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发表时间：
1997-06-30
期刊：
影响因子：
--
通讯作者：
Bloom GS
中科院分区：
文献类型：
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作者：
Bashour AM;Fullerton AT;Hart MJ;Bloom GS
已知GTP酶的活化形式Rac和Cdc 42分别刺激富含微生物活性的板状伪足和丝状伪足的形成，但其潜在机制仍不清楚。我们现在报告的蛋白质，IQGAP 1，这是可能介导的影响，这些GTP酶对微丝的纯化和表征。从牛肾上腺纯化的天然IQGAP 1包含两个190 kD亚基/分子加上亚化学计量的钙调蛋白。纯化的IQGAP 1直接绑定到F-肌动蛋白和交联的肌动蛋白丝成不规则的，相互连接的束，表现出凝胶样的性能。外源性钙调素部分抑制IQGAP 1与F-肌动蛋白的结合，并且在没有钙的情况下比在钙的存在下更有效。免疫荧光显微镜显示细胞松弛素D敏感的IQGAP 1与皮质微丝共定位。这些结果，结合先前的证据表明，IQGAP 1直接结合到激活的Rac和Cdc 42，表明IQGAP 1作为这些GTP酶和肌动蛋白细胞骨架之间的直接分子连接，并且IQGAP 1的肌动蛋白结合活性受钙调蛋白调节。
Activated forms of the GTPases, Rac and Cdc42, are known to stimulate formation of microfilament-rich lamellipodia and filopodia, respectively, but the underlying mechanisms have remained obscure. We now report the purification and characterization of a protein, IQGAP1, which is likely to mediate effects of these GTPases on microfilaments. Native IQGAP1 purified from bovine adrenal comprises two ∼190-kD subunits per molecule plus substoichiometric calmodulin. Purified IQGAP1 bound directly to F-actin and cross-linked the actin filaments into irregular, interconnected bundles that exhibited gel-like properties. Exogenous calmodulin partially inhibited binding of IQGAP1 to F-actin, and was more effective in the absence, than in the presence of calcium. Immunofluorescence microscopy demonstrated cytochalasin D–sensitive colocalization of IQGAP1 with cortical microfilaments. These results, in conjunction with prior evidence that IQGAP1 binds directly to activated Rac and Cdc42, suggest that IQGAP1 serves as a direct molecular link between these GTPases and the actin cytoskeleton, and that the actin-binding activity of IQGAP1 is regulated by calmodulin.