The Science Seminar Series: September 10, 2009
Characterization of the Xenorhabdus nematophila colonization protein NilB
Dr. Archna Bhasin
Department of Biology
Time: 4:00 -5:00pm
The bacterium Xenorhabdus nematophila mutualistically colonizes the intestinal vesicle of the nematode Steinernema carpocapsae. The X. nematophila gene nilB (nematode intestinal localization) is essential for S. carpocapsae nematode colonization. Since nilB has no apparent homologues to genes of known function, we undertook a structure-function analysis of this novel protein to determine its function in nematode colonization. NilB is a 55 kD, 466 amino acid protein containing a signal sequence predicted to target it to the membrane. It is also predicted to be an outer-membrane beta-barrel protein with a globular domain, 14 trans-membrane domains, 7 external loops and 6 periplasmic loops. FLAG (DYKDDDDK) tags were inserted at various locations including the N-terminus (after the signal sequence), the globular domain, the external loops as well as the C-terminus. These tagged mutants were analyzed for NilB protein production and for colonization competency. The most interesting mutant contains the FLAG insertion at amino acid 393 (loop 6), produces protein, but is colonization defective. This suggests that external loop 6 of NilB is required for interaction with the nematode intestinal vesicle.