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Research Interests

OVERVIEW

Research in our lab aims at understanding protein function on the basis of atomic structure determination using X-ray crystallography as an important tool. Our focal point is the elucidation of the structure and function of the Nuclear Pore Complex (NPC), the gateway into and out of the cell’s nucleus and thus of central importance for separating transcription and translation. We employ an integrative approach to this research area combining structure determination with biochemical, biophysical, cell biological and genetic methods.


RESEARCH SUMMARY

The Nuclear Pore Complex: In eukaryotes, genes are transcribed from DNA into RNA in the nucleus, whereas proteins are synthesized in the cytoplasm. For mRNA transcripts to exit the nucleus and protein molecules to enter back in they need to traverse the double-layered nuclear envelope membrane. This highly controlled process is exclusively facilitated by the NPC, a vast protein assembly that resides in circular openings in the nuclear envelope (Figure top right). We are trying to understand the workings of this nanomachine. To do so, we first attempt to solve the structure of the NPC. Multiple copies of about 30 different proteins (nucleoporins or nups), in total ~500 individual molecules or 40-60MDa in mass, make up an NPC. Nups are organized into distinct subcomplexes that assemble to form the entire structure (Figure below). In combining X-ray crystallographic techniques, amenable to the study of these subcomplexes, with electron-microscopic methods applied to larger assemblies, we are visualizing the NPC. So far our results have led to a detailed picture of the modular nature of the NPC and we have elucidated important design principles, all based on experimental evidence. Combining structural data with computational methods we established the evolutionary relationship between the NPC and vesicle coats, notably COP II, dating back more than one billion years and largely disguised on the primary sequence level. Several architectural nucleoporins share a common helical 65 kDa domain, the ancestral coatomer element ACE1, with Sec31, an essential component of the COP II coat. We expect to find more commonalities with the vesicle transport machinery and it will be interesting to see how these evolutionary relationships unravel.

Despite this progress, much work needs to be done to fully understand the NPC assembly. Yet, we can now already use the gained structural information to engineer probes that allow for dissecting NPC function in unprecedented precision. A myriad of functions besides its role in transport, for example in nuclear organization and gene regulation, place the NPC in the center of cell biology. Yet, these functions are so far only vaguely understood and represent major directions we are interested in exploring in the future.

Nuclear Pore Complexes (blue) on nuclei of baker’s yeast visualized by scanning electron microscopy. The NPC has a diameter of 100nm. Photograph kindly provided by Elena Kiseleva.

Composite crystal structure of the heptameric Y-complex (~ 0.6 MDa), one of the major components of the NPC. Its branched topology, together with other evidence, suggests a lattice-like NPC scaffold. Based on several recent papers published by the lab.

Schematic representation of the organization of nucleoporins into subcomplexes. The stable architectural core is shown in blue. (Brohawn et al., Structure, 2009)

massachusetts institute of technology, cambridge, ma - schwartz lab | tel: 1.617.452.3851 | tus@mit.edu