PhD ceremony: ms. K.B. Moscicka, 13.15 uur, Academiegebouw, Broerstraat 5, Groningen
Thesis: Structural investigation of membrane proteins by electron microscopy
Promotor(s): prof. E.J. Boekema
Faculty: Mathematics and Natural Sciences
Biological membranes are important components of all living organisms and they form the boundaries of cells and their organelles. Intact membrane complexes or purified proteins can be studied by using electron microscopy (EM) and the taken pictures can be later processed. Picture processing is very suitable for large flexible membrane proteins, and this thesis gives several examples of that.
First part of this thesis presents the study concerning peroxins. These are proteins which are involved in the import of the other proteins into peroxisomes. The model organism Hansenula polymorpha was used to purified PEX proteins. It appears that Pex5p protein have tetrameric structure; these tetramers are able to form a complexes with Pex20p protein. We show that Pex5p-Pex20p complex is able to change its conformation from a closed one to an open one with a diameter of 134 Å. The complex is also able to bind native catalase protein. We assumed that Pex5p-Pex20p complex is the functional receptor complex.
Another part of the thesis concerns three secondary transport proteins, such as CitS from Klebsiella pneumoniae and GltS from Escherichia coli. Both transporters prove to form dimers. We have made an overall model for the position of the monomers in the CitS dimer.
Finally we have studied the structure of the PilQ secretion complex of the bacteria Neisseria gonorrhoeae and Neisseria meningitidis. We have examined this complex in isolated outside membranes, without purifying it further. Our results helped us to determine the structure of extra domains which we could not observe in the purified complexes.
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