HI0381 of Haemophilus influenzae was investigated by circular dichroism (CD) and nuclear magnetic resonance (NMR) spectroscopy. HI0381 is a 153-residue peptidoglycan-associated outer membrane lipoprotein, and a part of the larger Tol/Pal network. Here, we report its backbone 1H, 15N, and 13C resonance assignments, and secondary structure predictions. About 97% of all of the 1HN, 15N, 13CO, 13C?, and 13C? resonances covering 131 non-proline residues of the 134 residue, mature protein, were clarified by sequential and specific assignments. CSI and TALOS analyses revealed that HI0381 contains five ?-helices and five ?-strands. To characterize the structure of HI0381, the effects of pH and salt concentration were investigated by CD. In addition, the structural changes occurring when HI0381 was in a membranous environment were investigated by comparing its HSQC spectra and CD data in buffer and in DPC micelles; the results showed that helix α4 and strand ?4 became aligned with the membrane. We conclude that the conformation of HI0381 is affected by the membrane environment, implying that its folded state is directly related to its function.

Keywords: Haemophilus influenzae, NMR, peptidoglycan-associated lipoprotein (Pal protein), HI0381, Tol-Pal system