Final Report Summary - MICROTUBULE PLUS END (Structural and kinetic basis of evolutionary conserved and divergent microtubule plus end tracking mechanisms) Introduction The microtubule cytoskeleton is of crucial importance for many essential cellular functions such as establishing cell morphology, intracellular transport, chromosome segregation during cell division and cell motility. Failures in these processes can result in promotion of cancer and developmental diseases. Microtubules are structurally polar tubes made of protofilaments assembled from proteins called alpha / beta-tubulin. Tubulin is incorporated into microtubules with guanosine triphosphate proteins (GTP) bound to its beta-subunit. During microtubule assembly GTP is hydrolysed; this reaction is ultimately responsible for the property of microtubules to randomly switch between phases of growth and shrinkage, a behaviour termed dynamic instability. It is essential for the ability of microtubules to explore intracellular space, to rapidly reorganise their distribution and to contribute to generating the pushing and pulling forces that move chromosomes during cell division. Critical decisions between microtubule assembly and disassembly take place at microtubule ends. End-binding proteins (EBs) bind there to a region with so far unknown structural characteristics. EBs recruit a variety of other factors, thereby constituting the core of a versatile protein interaction network, which allows the cell to shape and control their microtubule cytoskeleton. Results To better understand how EBs interact with microtubule ends, we examined the structural characteristics of this interaction. Using cryo-electron microscopy, subnanometre single-particle reconstruction, and fluorescence microscopy imaging, we discovered that EBs bridge microtubule protofilaments at a position that is right next to the beta-tubulin GTPase site. That is of interest, because this binding site positions them ideally to sense GTP hydrolysis. We further found that the region recognised by EBs functions as a stabilising structural cap which protects microtubules from disassembly, thus allowing them to have extended episodes of continuous growth. Taken together, our findings establish a structural link between two important biological phenomena, microtubule dynamic instability and microtubule end tracking by EBs. Related documents Final Report - MICROTUBULE PLUS END (Structural and kinetic basis of evolutionary conserved and divergent microtubule plus end tracking mechanisms)
