End-binding proteins
End-binding proteins (EBs) are proteins from the family of + TIP proteins , which belong to the microtubule-associated proteins (MAPs) , and are found in human cells. They interact with the microtubules as well as with cellular structures.
construction
There are three EBs or EB1-like structures in the human organism: EB1, EB2 and EB3. They are smaller dimers , each monomer of which contains two conserved and interconnected domains. The highly conserved calponin homology (CH) domain on the outside binds to the microtubules and detects their growing ends. There is a coiled coil domain at the carboxyl terminus of the proteins . This is responsible for homo- and heterodimerization . Its end consists of a four-helix bundle with a hydrophobic cavity and a polar edge. The EB homology (EBH) domain, also called EB1-like motif, regulates the interactions of the EB proteins with other + TIPs. The C-terminus is followed by an EEY / F motif, the amino acids of which are homologous to those of the C-terminus of certain tubulins and + TIPs and are used for binding to other proteins.
function
Because of their ability to bind directly to the rapidly growing microtubules, EBs can quickly recruit additional + TIPs. EB proteins recognize the microtubule plus ends and play an important role there in the attachment of further units via dimerization. The C-terminus of these proteins contains a coiled-coil domain, which brings about the dimerization of the EB molecules. It is presumably this structure that recognizes the specific ends of the growing microtubule ends. Although the exact binding site on the microtubule is not yet known, the EB proteins are said to be the main integrators in the protein interaction network and its structure. Further components enable the EBs to guide the + TIPs to the microtubule ends. They can recognize the growing ends of the microtubules independently of their binding partners and dock directly through their N-terminal CH domain. Other domains bind other + TIPs. Since the functions and properties of EBs varied greatly in numerous experiments, the function in the regulation of microtubule dynamics is largely unexplained. Normally these proteins increase the growth in cells and reduce the catastrophe rate, they also play an important role in the formation of the network of + TIPs. There were large differences in the results in experiments. The sometimes contradicting results of in-vivo and in-vitro experiments were attributed to the different initial states of the proteins, for example to the purified samples compared to unchanged in-vitro samples.
Individual evidence
- ↑ a b c d e f g Julia Arens: The role of microtubule-regulating proteins during neuronal differentiation , 2012, Technical University Dortmund, Max Planck Institute for Molecular Physiology.
- ↑ a b c d e f cell.com: Plus-End-Tracking Proteins and Their Interactions at Microtubule Ends, last accessed January 22, 2016