FrpD is a highly conserved lipoprotein of Neisseria meningitidis anchored to the bacterial outer membrane. The frpD gene sequence contains two translation initiation sites, which give rise to production of the full-length FrpD protein (FrpD271) that harbours N-terminal signal peptide promoting FrpD export across the cytoplasmic membrane by Sec translocase, and the truncated FrpD protein (FrpD250) that lacks the signal peptide and remaining in cytoplasm of the bacteria. The exported FrpD271 precursor is processed to its mature form on the periplasmic side of the cytoplasmic membrane, sequentially modified by a lipid molecule at Cys25 residue, and sorted to the outer bacterial membrane . The biological function of FrpD appears to be linked to the FrpC protein, since FrpD was found to bind the N-terminal part of FrpC with very high affinity (Kd = 0.2 nM) . However, mechanism of FrpD-FrpC interaction is unknown due to the absence of any structural information on these proteins.
We present here the crystal and solution structures of the FrpD protein and the NMR spectroscopy identification of the FrpD43-271-FrpC1-414 interaction interface. According to the detailed structure analysis, the atomic structures of FrpD reveal a novel protein fold. This structural information provides the first step in deciphering of the mechanism of FrpD43-271-FrpC1-414 interaction and sets the base for further investigation of the role of FrpD in the N. meningitidis lifestyle.