Tag–probe labeling methods for live-cell imaging of membrane proteins

Multifaceted nature of membrane microdomains in colorectal cancer

Membrane microdomains or lipid rafts are known to be highly dynamic and to act as selective signal transduction mediators that facilitate interactions between the cell’s external and internal environments. Lipid rafts play an important mediating role in the biology of cancer: they have been found in almost all existing experimental cancer models, including colorectal cancer (CRC), and play key regulatory roles in cell migration, metastasis, cell survival and tumor progression. This paper explores the current state of knowledge in this field by highlighting some of the pioneering and recent lipid raft studies performed on different CRC cell lines and human tissue samples. From this literature review, it becomes clear that membrane microdomains appear to be implicated in all key intracellular signaling pathways for lipid metabolism, drug resistance, cell adhesion, cell death, cell proliferation and many other processes in CRC. All signal transduction pathways seem to originate directly from those peculiar lipid islands, thereby orchestrating the colon cancer cells’ state and fate. As confirmed by recent animal and preclinical studies in different CRC models, continuing to unravel the structure and function of lipid rafts - including their associated complex signaling pathways - will likely bring us one step closer to better monitoring and treating of colon cancer patients.

Covalent quantum dot receptor linkage via the acyl carrier protein for single-molecule tracking, internalization, and trafficking studies

Here we describe a labeling technique for the covalent linkage of quantum dots to transmembrane receptors for single-molecule tracking. Our method combines the acyl carrier protein (ACP) technique with coenzyme A (CoA)—functionalized quantum dots to covalently attach quantum dots to ACP fusions of receptor proteins. The advantages of this approach include: (i) the use of a smaller attachment linker than in many other quantum dot—labeling systems; (ii) the ability to achieve a reliable 1:1 fluorophore-to-receptor labeling stoichiometry; (iii) the specificity of the method; and (iv) the covalent nature of the quantum dot linkage. We demonstrate the general suitability of this technique in single-molecule tracking, internalization, and trafficking studies by imaging two different transmembrane receptors in living cells.

Tricks of the trade used to accelerate high-resolution structure determination of membrane proteins

The rate at which X-ray structures of membrane proteins are solved is on a par with that of soluble proteins in the late 1970s. There are still many obstacles facing the membrane protein structural community. Recently, there have been several technical achievements in the field that have started to dramatically accelerate structural studies. Here, we summarize these so-called 'tricks-of-the-trade' and include case studies of several mammalian transporters.