Dissertaties - Rijksuniversiteit Groningen
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The type IV secretion and the type IV pili Systems of Neisseria gonorrhoeae

(2011) Jain, Samta

Members of the type IV secretion system (T4SS) and the type IV pili (Tfp) systems of the human pathogen Neisseria gonorrhoeae are studied in this thesis. T4SS are multiprotein complex involved in conjugation, substrate/toxin secretion and DNA uptake or release. The T4SS in N. gonorrhoeae is encoded by the horizontally acquired gonococcal genetic island (GGI) that functions to secrete DNA into the medium. The mechanism of pilus processing of the pilin protein TraA encoded by the GGI was investigated. It was found that after co-translation membrane insertion, TraAGGI is cleaved by leader peptidase and circularized by the pilus processing protein TrbIGGI. T4SSs encodes a pilot protein called relaxase that binds, cleaves and transports DNA to the recipient organism. The study of the novel family of relaxase TraI of GGI revealed the presence of three distinct features; an N-terminal hydrophobic domain, an HD domain of the metal-dependent phosphohydrolase family and a C-terminal DUF 1528 domain. GGI also encodes a single stranded DNA binding protein called SsbB, the function and biochemistry of this protein was investigated. SsbBGGI bound DNA in a magnesium independent non-cooperative manner and stimulated topoisomerase I activity in vitro. In prokaryotes, Tfp systems function in motility, adhesion and DNA uptake. The PilQ proteins of the Tfp system belong to secretin superfamily that forms oligomeric integral outer membrane complexes for the translocation of macromolecules. Previously unidentified large and flexible extra domains were observed during the study of PilQ secretin complex in the native membrane environment of pathogenic Neisseria.

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