Biochemical analysis of human IQGAP proteins

在你的细胞中有一个叫做细胞骨架的蛋白质网络。这不是一个很好的名字，因为它不像你的骨头，它不断地被拆开，重新组装，四处移动。它的作用是为细胞提供支持，为细胞内的物质运动提供轨道并帮助细胞运动。所有这些活动都需要协调，如果出现问题，你就会生病。你甚至可能得癌症。最近最有趣的发现之一是，有一组蛋白质的作用是帮助组织细胞骨架。这些组织蛋白（被称为支架蛋白）所做的不仅仅是在正确的时间将正确的蛋白质聚集在一起。它们还通过粘在其他蛋白质上与它们对话。当两种蛋白质相互粘在一起时，由于分子可以采用不同的形状，信息可以在它们之间传递。所以我们认为这些支架蛋白会倾听其他蛋白质所说的话，弄清楚它们的意思，然后将正确的信息传递给细胞骨架。你可以把它们想象成微型电话交换机。我们想知道它们是如何工作的。我们感兴趣的特殊支架蛋白被称为IQGAP蛋白。人体内有三种不同类型的IQGAP1、IQGAP2和IQGAP3。别担心/ IQGAP这个名字并不意味着你愚蠢，因为你的智商有差距。它实际上是以蛋白质的两个部分命名的iq基序和GAP结构域。这是粘在其他蛋白质上的两种蛋白质。iq基序附着在一种叫做钙调蛋白的蛋白质上，GAP结构域附着在一种叫做CDC42的蛋白质上。钙调蛋白和CDC42都是在细胞内传递信息的蛋白质。还有一个我们感兴趣的部位叫做CHD它附着在肌动蛋白上。肌动蛋白是细胞骨架中的一种蛋白质。因此，我们认为iqgap从钙调蛋白和CDC42收集信息，并将其传递给肌动蛋白。我们想知道他们是怎么做到的。我们要做的是对一些细菌进行基因工程改造，这样它们就会为我们制造钙调蛋白和CDC42。iqgap有点大，所以我们会做一些片段。幸运的是，其他科学家已经发现了一些细菌乐于制造的碎片。肌动蛋白也有问题。其他人已经证明，当细菌产生这种蛋白质时，它不能正常工作。所以我们用酵母代替。一旦我们得到了所有这些蛋白质，我们就会问它们是如何粘在一起的。我们会试着找出蛋白质粘在一起的地方发生的化学细节。当然，蛋白质非常非常小，所以我们不能只看它们。我们甚至不能在显微镜下观察它们。所以我们必须使用间接的方法使用化学和物理来找出发生了什么。我们还将使用化学和物理方法来了解它们的粘附程度。我们非常感兴趣的另一件事是IQGAP1、IQGAP2和IQGAP3彼此之间有何不同。我们知道它们非常相似，但我们也知道IQGAP1和IQGAP2存在于不同的细胞中，并且粘附在其他蛋白质的范围略有不同。至于IQGAP3，我们真的还不知道。所以我们对它的任何发现都将是新颖的。我们认为，每个IQGAP粘附在这些其他蛋白质上的方式会略有不同，它们粘附的强度也会有所不同。希望一旦我们知道了它们如何粘在一起的化学细节，我们也能很好地了解为什么粘的强度是不同的。这个项目很重要，因为细胞骨架在许多疾病中出现问题，一些药物与细胞骨架相互作用。当我们完成时，我们将更接近于理解这些微小的分子电话交换是如何工作的。

In your cells there is a network of proteins called the cytoskeleton. This isn't a very good name because unlike your bones it is constantly being taken apart, put back together and moved around. Its job is to provide support for the cell, to provide tracks for things to move about in the cell on and to help the cell move around. All these activities need to be co-ordinated and if this goes wrong you'll get ill. You might even get cancer. One of the most interesting recent discoveries is that there are a group of proteins whose job it is to help organise the cytoskeleton. These organising proteins (called scaffolding proteins) do more than just bring the right proteins together at the right time. They also talk to other proteins by sticking to them. When two proteins stick to each other messages can be passed between them because of the different shapes the molecules can adopt. So we think these scaffolding proteins listen to what other proteins have to say, work out what it all means and then pass the right message on to the cytoskeleton. You can think of them being like miniature telephone exchanges. We want to know how they work. The particular scaffolding proteins we are interested in are called the IQGAP proteins. In your body you have three different types of IQGAP protein called IQGAP1, IQGAP2 and IQGAP3. Don't worry / the name IQGAP doesn't mean that you're stupid because you have a gap in your IQ. It's actually named after two parts of the protein / the IQ-motifs and the GAP domain. These are two of the bits of the protein which stick to other proteins. The IQ-motifs stick to a protein called calmodulin and the GAP domain to one called CDC42. Both calmodulin and CDC42 are proteins which carry messages round the cell. There's another bit we're interested in called the CHD which sticks to actin. Actin is a protein in the cytoskeleton. So we think IQGAPs collect information from calmodulin and CDC42 and pass it on to actin. We want to find out how they do that. What we're going do is to genetically engineer some bacteria so that they'll make calmodulin and CDC42 for us. IQGAPs are a bit big to do this with and so we'll make fragments of them. Luckily for us, other scientists have already worked out some fragments which bacteria are happy to make. We've also got a problem with actin. Other people have shown that when bacteria make this protein it doesn't work properly. So we'll make that one in yeast instead. Once we've got all these proteins we'll ask how they stick together. We'll try and find out the chemical details of what's going on at the places where the proteins stick together. Of course proteins are very very small and so we can't just look at them. We can't even look at them under a microscope. So we have to use indirect methods using chemistry and physics to find out what's going on. We're also going to find out how tightly they stick / again using chemical and physical methods. Another thing we're very interested in is how IQGAP1, IQGAP2 and IQGAP3 differ from each other. We know that they are quite similar, but we also know that IQGAP1 and IQGAP2 are found in different cells and stick to a slightly different range of other proteins. As for IQGAP3 we really don't know anything about that yet. So anything we discover about it really will be novel. We think that the way each IQGAP sticks to these other proteins will be slightly different and that how strongly they stick will also be different. Hopefully once we know the chemical details about how they stick, we'll also have a good idea about why the strength of stickiness is different. This project is important because the cytoskeleton goes wrong in a lot of diseases and some drugs interact with the cytoskeleton. When we've finished we'll be a bit closer to understanding how these tiny molecular telephone exchanges actually work.