Alkylgold complexes by the intramolecular aminoauration of unactivated alkenes

Alkylgold(I) complexes were formed from the gold(I)-promoted intramolecular addition of various amine nucleophiles to alkenes. These experiments provide the first direct experimental evidence for the elementary step of gold-promoted nucleophilic addition to an alkene. Deuterium-labeling studies and X-ray crystal structures provide support for a mechanism involving anti-addition of the nucleophile to a gold-activated alkene, which is verified by DFT analysis of the mechanism. Ligand studies indicate that the rate of aminoauration can be drastically increased by use of electron-poor arylphosphines, which are also shown to be favored in ligand exchange experiments. Attempts at protodeauration lead only to recovery of the starting olefins, though the gold can be removed under reducing conditions to provide the purported hydroamination products

Structural and biochemical characterization of nuclear pore complex structural scaffold sub-complexes

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biology, 2017Cataloged from PDF version of thesis.Includes bibliographical references.The nuclear pore complex (NPC) is a large, modular protein assembly that regulates nucleocytoplasmic transport in all eukaryotes. The ~60-120 MDa NPC is a modular assembly of multiple copies of ~30 distinct proteins that are arranged into biochemically distinct sub-complexes. We believe that the structural characterization of the NPC is essential for understanding its transport mechanisms and various pathologies and human diseases associated with deletions or mutations of constituents. To obtain detailed structural information of the NPC, techniques that span several resolution ranges are necessary due to its large size and complexity. For instance, recent progress in the structural characterization of the overall architecture of the NPC by cryo-electron tomography(cryo-ET) to ~23Å resolution has revealed its size, shape, and course arrangement, but lacks distinguishable protein-protein boundaries and secondary structural details.Although the entire NPC is not amenable to high resolution X-ray crystallography, we complement the cryo-ET reconstructions with a divide and conquer approach by obtaining high resolution X-ray crystal structures of individual subcomplexes. By taking advantage of the modular nature of the NPC, we can dock subcomplexes into the cryo-ET reconstructions to identify their location within the NPC. This composite structure will bridge the meso resolution cryo-ET reconstructions of the entire NPC and the incomplete but high resolution X-ray crystal structure of individual subcomplexes. As a first step towards understanding the detailed organization of the NPC, our goal is to solve the high resolution structures of the two principal structural scaffold subcomplexes, the Y and Nic96 complexes. In this study, we present the high resolution composite X-ray crystal structure of the Y complex.Docking the composite model into previously solved random conical tilt(RCT) and tomographic reconstructions of negatively stained samples of the Y complex shows overall consistency between the three methods, yet we highlight important structural differences that constrain possible arrangements of multiple Y complexes within the NPC. By docking the composite model into the cryo-ET reconstructions of the entire NPC, we propose an arrangement of multiple Y complexes that is consistent with our composite structure. In addition, progress on structurally characterizing the Nic96 complex will be presented. Preliminary results suggest that Nup1 92 and Nic96 form a flexible, yet semi-ordered interface. Future directions for characterizing the rest of the Nic96 complex, including current challenges and suggestions will be discussed.by Kotaro Kelley.Ph. D.Ph.D. Massachusetts Institute of Technology, Department of Biolog

Topaz-Denoise: general deep denoising models for cryoEM and cryoET

The low signal-to-noise ratio (SNR) in cryoEM images can make the first steps in cryoEM structure determination challenging, particularly for non-globular and small proteins. Here, the authors present Topaz-Denoise, a deep learning based method for micrograph denoising that significantly increases the SNR of cryoEM images and cryoET tomograms, which helps to accelerate the cryoEM pipeline

Atomic structure of the Y complex of the nuclear pore

available in PMC 2015 November 01The nuclear pore complex (NPC) is the principal gateway for transport into and out of the nucleus. Selectivity is achieved through the hydrogel-like core of the NPC. The structural integrity of the NPC depends on ~15 architectural proteins, which are organized in distinct subcomplexes to form the >40-MDa ring-like structure. Here we present the 4.1-Å crystal structure of a heterotetrameric core element ('hub') of the Y complex, the essential NPC building block, from Myceliophthora thermophila. Using the hub structure together with known Y-complex fragments, we built the entire ~0.5-MDa Y complex. Our data reveal that the conserved core of the Y complex has six rather than seven members. Evolutionarily distant Y-complex assemblies share a conserved core that is very similar in shape and dimension, thus suggesting that there are closely related architectural codes for constructing the NPC in all eukaryotes.National Institute of General Medical Sciences (U.S.) (award GM103403)National Institutes of Health (U.S.)National Science Foundation (U.S.) (NSF Graduate Research Fellowship Program, grant 1122374)National Institutes of Health (U.S.) (NIH Grant R01GM77537)National Institutes of Health (U.S.) (NIH Grant T32GM007287

The structure of natively iodinated bovine thyroglobulin

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/171011/1/ayd2jb5028.pd