positions for postdoctoral fellows

[Jim Hogle]

We have openings for one or two postdocs with experience with cryo 
electron microscopy and image reconstruction methods to study the cell 
entry mechanism of poliovirus and related picornaviruses.

Over the years we have solved the structure of the virus and a key 
assembly intermediate at high resolution by x-ray crystallography, and 
in collaboration with David Belnap and Alasdair Steven at NIH we have 
solved the structures of the virus-receptor complex and of an early 
cell entry intermediate at intermediate resolution (currently ~10Å) and 
of the final product of the entry pathway at moderate resolution (~20Å) 
by cryo electron microscopy.  These structures together with ongoing 
work in our laboratory and elsewhere has led to a working model for 
poliovirus cell entry in which receptor mediated conformational changes 
result in the exposure of hydrophobic sequences (including a small 
myristylated protein VP4 and the N-terminus of the capsid protein VP1) 
that are inserted in the membrane to form a channel which allows the 
viral RNA genome to cross the cell membrane and enter the cytoplasm 
(Hogle (2002) Ann. Rev. Microbiol. 56, 677-702).

In order to test this model, we have developed a simple liposome-based 
model system that allows the efficient incorporation of receptors, 
virus binding, and induces the receptor-mediated conformational changes 
to produce a stable complex between the altered virus and the membrane. 
  We have initiated structural studies of the virus-receptor-liposome 
complex with the virus and receptor on the outside of the liposome 
(mimicking the initial virus cell complexes) using multiple particle 
reconstruction techniques with very promising initial results.  In 
collaboration with the Boulder Laboratory for 3D Microscopy of Cells, 
we have also initiated cryotomographic studies of the virus-receptor 
liposome complexes and are working on approaches that will allow us to 
average over multiple tomographic reconstructions of the complex.   We 
have planned parallel studies of the altered-virus-liposome complex 
(with a goal of visualizing the channel), and virus-receptor-liposome 
and altered virus – liposome complexes in which the virus is on the 
inside of the liposome (mimicking virus in internalized vesicles).  
These studies will be carried out in parallel with ongoing optical 
microscopy studies in both live and fixed cells.

The lab has access to state-of-the-art microscopy (Tecnai F12, F20, and 
F30 microscopes) and computational facilities.

If you are interested please send a CV and names of references to Jim 
Hogle at jhogle at hms.harvard.edu.
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