The membrane protein universe: what's out there and why bother?

Chances are that you have come across membrane proteins many times in your professional life: ion channels, aquaporins, G-protein-coupled receptors, drug resistance proteins. But it is also quite likely that you have never bothered to think about what the implications are of being a membrane protein, as opposed to a soluble protein. What is special about membrane proteins in terms of structure and function, how many membrane proteins are out there, how are they made in the cell? Welcome to the membrane protein universe!.