The trimeric periplasmic chaperone Skp of XXXX forms 1:1 complexes with outer membrane proteins via hydrophobic and electrostatic interactions.

@entity1 @entity20600 @entity8209 @entity2340 @entity3323 @entity526
The interactions of outer membrane proteins (OMPs) with the periplasmic chaperone Skp from @entity526 are not well understood. We have examined the binding of Skp to various OMPs of different origin, size, and function. These were OmpA, OmpG, and YaeT (Omp85) from @entity526 , the translocator domain of the autotransporter NalP from Neisseria meningitides, FomA from @entity8209 , and the voltage-dependent anion-selective channel, @entity1 isoform 1 ( @entity20600 ) from mitochondria. Binding of Skp was observed for bacterial OMPs, but neither for @entity20600 nor for soluble bovine serum albumin. The Skp trimer formed 1:1 complexes, OMP.Skp(3), with bacterial OMPs, independent of their size or origin. The dissociation constants of these OMP.Skp(3) complexes were all in the nanomolar range, indicating that they are stable. Complexes of Skp(3) with YaeT displayed the smallest dissociation constants, complexes with NalP the largest. OMP binding to Skp(3) was pH-dependent and not observed when either Skp or OMPs were neutralized at very basic or very acidic pH. When the ionic strength was increased, the free energies of binding of Skp to OmpA or OmpG were reduced. Electrostatic interactions were therefore necessary for formation and stability of OMP.Skp(3) complexes. Light-scattering and circular dichroism experiments demonstrated that Skp(3) remained a stable trimer from pH 3 to pH 11. In the OmpA.Skp(3) complex, Skp efficiently shielded @entity2340 residues of the transmembrane strands of OmpA against fluorescence quenching by aqueous @entity3323 . Lipopolysaccharide (LPS), a major component of the outer membrane of Gram-negative bacteria, bound to OmpA.Skp(3) complexes at low stoichiometries. @entity3323 quenching of fluorescence indicated that in this ternary complex, the @entity2340 residues of the transmembrane domain of OmpA were located closer to the surface than in binary OmpA.Skp(3) complexes. This may explain previous observations that folding of Skp-bound OmpA into lipid bilayers is facilitated in presence of LPS.
