@article {47562, title = {Design of a hyperstable 60-subunit protein icosahedron.}, journal = {Nature}, year = {2016}, month = {2016 Jun 15}, abstract = {

The icosahedron is the largest of the Platonic solids, and icosahedral protein structures are widely used in biological systems for packaging and transport. There has been considerable interest in repurposing such structures for applications ranging from targeted delivery to multivalent immunogen presentation. The ability to design proteins that self-assemble into precisely specified, highly ordered icosahedral structures would open the door to a new generation of protein containers with properties custom-tailored to specific applications. Here we describe the computational design of a 25-nanometre icosahedral nanocage that self-assembles from trimeric protein building blocks. The designed protein was produced in Escherichia coli, and found by electron microscopy to assemble into a homogenous population of icosahedral particles nearly identical to the design model. The particles are stable in 6.7 molar guanidine hydrochloride at up to 80 degrees Celsius, and undergo extremely abrupt, but reversible, disassembly between 2 molar and 2.25 molar guanidinium thiocyanate. The icosahedron is robust to genetic fusions: one or two copies of green fluorescent protein (GFP) can be fused to each of the 60 subunits to create highly fluorescent {\textquoteright}standard candles{\textquoteright} for use in light microscopy, and a designed protein pentamer can be placed in the centre of each of the 20 pentameric faces to modulate the size of the entrance/exit channels of the cage. Such robust and customizable nanocages should have considerable utility in targeted drug delivery, vaccine design and synthetic biology.

}, issn = {1476-4687}, doi = {10.1038/nature18010}, author = {Hsia, Yang and Bale, Jacob B and Gonen, Shane and Shi, Dan and Sheffler, William and Fong, Kimberly K and Nattermann, Una and Xu, Chunfu and Huang, Po-Ssu and Ravichandran, Rashmi and Yi, Sue and Davis, Trisha N and Gonen, Tamir and King, Neil P and Baker, David} } @article {5153, title = {The Ndc80 kinetochore complex directly modulates microtubule dynamics.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {109}, year = {2012}, month = {2012 Aug 20}, pages = {16113-8}, abstract = {

The conserved Ndc80 complex is an essential microtubule-binding component of the kinetochore. Recent findings suggest that the Ndc80 complex influences microtubule dynamics at kinetochores in vivo. However, it was unclear if the Ndc80 complex mediates these effects directly, or by affecting other factors localized at the kinetochore. Using a reconstituted system in vitro, we show that the human Ndc80 complex directly stabilizes the tips of disassembling microtubules and promotes rescue (the transition from microtubule shortening to growth). In vivo, an N-terminal domain in the Ndc80 complex is phosphorylated by the Aurora B kinase. Mutations that mimic phosphorylation of the Ndc80 complex prevent stable kinetochore-microtubule attachment, and mutations that block phosphorylation damp kinetochore oscillations. We find that the Ndc80 complex with Aurora B phosphomimetic mutations is defective at promoting microtubule rescue, even when robustly coupled to disassembling microtubule tips. This impaired ability to affect dynamics is not simply because of weakened microtubule binding, as an N-terminally truncated complex with similar binding affinity is able to promote rescue. Taken together, these results suggest that in addition to regulating attachment stability, Aurora B controls microtubule dynamics through phosphorylation of the Ndc80 complex.

}, issn = {1091-6490}, doi = {10.1073/pnas.1209615109}, author = {Umbreit, Neil T and Gestaut, Daniel R and Tien, Jerry F and Vollmar, Breanna S and Gonen, Tamir and Asbury, Charles L and Davis, Trisha N} } @article {3636, title = {Cooperation of the Dam1 and Ndc80 kinetochore complexes enhances microtubule coupling and is regulated by aurora B.}, journal = {The Journal of Cell Biology}, volume = {189}, year = {2010}, month = {2010 May 17}, pages = {713-23}, abstract = {

The coupling of kinetochores to dynamic spindle microtubules is crucial for chromosome positioning and segregation, error correction, and cell cycle progression. How these fundamental attachments are made and persist under tensile forces from the spindle remain important questions. As microtubule-binding elements, the budding yeast Ndc80 and Dam1 kinetochore complexes are essential and not redundant, but their distinct contributions are unknown. In this study, we show that the Dam1 complex is a processivity factor for the Ndc80 complex, enhancing the ability of the Ndc80 complex to form load-bearing attachments to and track with dynamic microtubule tips in vitro. Moreover, the interaction between the Ndc80 and Dam1 complexes is abolished when the Dam1 complex is phosphorylated by the yeast aurora B kinase Ipl1. This provides evidence for a mechanism by which aurora B resets aberrant kinetochore-microtubule attachments. We propose that the action of the Dam1 complex as a processivity factor in kinetochore-microtubule attachment is regulated by conserved signals for error correction.

}, keywords = {Cell Cycle Proteins, Green Fluorescent Proteins, Kinetochores, Microtubule-Associated Proteins, Microtubules, Mitotic Spindle Apparatus, Nuclear Proteins, Protein-Serine-Threonine Kinases, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins}, issn = {1540-8140}, doi = {10.1083/jcb.200910142}, author = {Tien, Jerry F and Umbreit, Neil T and Gestaut, Daniel R and Franck, Andrew D and Cooper, Jeremy and Wordeman, Linda and Gonen, Tamir and Asbury, Charles L and Davis, Trisha N} } @article {45961, title = {Tension applied through the Dam1 complex promotes microtubule elongation providing a direct mechanism for length control in mitosis.}, journal = {Nature Cell Biology}, volume = {9}, year = {2007}, month = {2007 Jul}, pages = {832-7}, abstract = {

In dividing cells, kinetochores couple chromosomes to the tips of growing and shortening microtubule fibres and tension at the kinetochore-microtubule interface promotes fibre elongation. Tension-dependent microtubule fibre elongation is thought to be essential for coordinating chromosome alignment and separation, but the mechanism underlying this effect is unknown. Using optical tweezers, we applied tension to a model of the kinetochore-microtubule interface composed of the yeast Dam1 complex bound to individual dynamic microtubule tips. Higher tension decreased the likelihood that growing tips would begin to shorten, slowed shortening, and increased the likelihood that shortening tips would resume growth. These effects are similar to the effects of tension on kinetochore-attached microtubule fibres in many cell types, suggesting that we have reconstituted a direct mechanism for microtubule-length control in mitosis.

}, keywords = {Biomechanical Phenomena, Cell Cycle Proteins, Fungal Proteins, Kinetochores, Microspheres, Microtubule-Associated Proteins, Microtubules, Mitosis, Optical Tweezers, Saccharomyces cerevisiae Proteins}, issn = {1465-7392}, doi = {10.1038/ncb1609}, author = {Franck, Andrew D and Powers, Andrew F and Gestaut, Daniel R and Gonen, Tamir and Davis, Trisha N and Asbury, Charles L} }