| Start Date: | 11/6/2014 | Start Time: | 4:30 PM |
| End Date: | 11/6/2014 | End Time: | 5:30 PM |
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Event Description
Tanja Mittag, PhD,
Structural Biology, St. Jude Children’s Research Hospital, Memphis, TN
"The role of protein self-association in organelle formation and ubiquitination"
Light microscopically detectable, non-membrane bound cellular “bodies”, such as nucleoli, P bodies and stress granules, have recently been characterized as large protein or protein/RNA assemblies with liquid droplet properties. Weak, multivalent protein interactions can result in liquid phase separation in vitro and may also form the foundation of cellular “bodies” with liquid-like properties. However, the specific interactions underlying their formation and their associated biochemical function(s) are mostly unclear. Here, we report that the punctate localization of speckle-type POZ protein (SPOP), a ubiquitin ligase substrate adaptor and recently identified tumor suppressor, depends upon the presence of two intact oligomerization domains. Using a variety of biophysical techniques, including analytical ultracentrifugation, size exclusion chromatography, light scattering and native mass spectrometry, we show here that two distinct dimerization domains in SPOP mediate the formation of concentration-dependent higher-order SPOP homo-oligomers. Their size distribution depends on the protein concentration. We demonstrate that one SPOP domain dimerizes with nanomolar affinity, resulting in dimers as the base-building block for higher-order self-association. The other domain dimerizes three orders of magnitude weaker, rendering SPOP oligomers highly dynamic. We describe the size distribution of higher-order SPOP oligomers, providing for the first time a quantitative picture of protein assemblies participating in the formation of cellular “bodies”. We also show that multivalent substrates co-localize in SPOP “bodies”. Together, these results suggest that SPOP nuclear “bodies”, may be mediated by (1) specific oligomerization through defined interfaces in SPOP; and (2) the weak multivalent interactions between Gli3/SPOP. Mutations in the SPOP oligomerization domains have been found in uterine, colorectal, skin, and brain cancers, highlighting the importance of SPOP self-association for its biological function. Our results provide insight into the fundamental mechanisms underlying cellular compartmentalization without membranes. |
Contact Information:
Name: Prof. Frank Ji
Phone: 215.895.2562
Email: hj56@drexel.edu |
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Location:
Disque Hall, Room 109, 32 South 32nd Street, Philadelphia, PA 19135 |
Audience:
AlumniCurrent StudentsFacultyGraduate Students |
Special Features:
Free Food |
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