EGFR – one protein’s story  pg. 2

Like the rest of the proteins in the cell, I was put together on one of the assembly lines. Earlier, I referred to us proteins as being like beaded necklaces. Here’s why. We are made of chemical “beads” called amino acids. Twenty different kinds of amino acid beads are strung
together in a particular order for each protein, based on a copy of the plans. So the blueprints might say something like: purple, green, green, blue, red, yellow, purple, yellow, blue …, really the DNA spells out the order of the amino acids, not colors of beads, but you get the idea. The
assembly line proteins read out the order, pick out the right amino acids, and put them together in long protein strings.

The order of the beads, then, makes each of us unique. The order determines what we do  and the shapes that we take. At the end of the manufacturing process, we don’t end up with our amino acids all in a tidy straight line. Instead, we coil and twist as we are made—with the help of folding proteins, until we look like hopelessly tangled necklaces. Scientists call this our structure. Though it may look like a globby mess, the bumps and dips in our structures are carefully constructed for the interactions we have with other proteins and molecules inside and outside the cell.

After we come off the assembly line, we load into a series of shuttles for transport to our job sites in the cell. En route, we can receive some additional decorations—flourishes added to some of our beads—like you might put on a scarf, or a hat. Our decorations are things like
sugars and fatty acid chains; they outfit us for our jobs. Because of varying accessories, even two EGF receptors might end up looking a little bit different from each other. We proteins, you see, are as individual as are you human beings.

So I made it out to the cell surface, along with a shuttle full of other proteins bound for  the same destination. As I told you, I am a receptor, which means my job is to receive incoming messages. Well, only certain arriving messages. I am specialized to respond to epidermal
growth factor (EGF) and a handful of other signals that are similar to EGF.

EGF—itself a protein, by the way—is one of the many messenger molecules that continuously bombard the outside of the cell. A few of these signal molecules can pass directly through the membrane, but most must interact with a receptor to have their message sent on.
Hundreds of different receptors, as well as other kinds of proteins, stud the cell surface. I am not the lone receiver of EGF signals—other EGF receptors and our family members join me in the task. Our family members actually work as pairs to send messages inside the cell.

When EGF sticks to us and we team up, we pass the signal along to a host of proteins inside the cell. These courier proteins are waiting nearby, just inside the walls, ready to take the message from us and speed off, transmitting it to parts deep inside the factory.

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