Structural Superimposition

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Periplasmic chaperones prevent misfolding and aggregation of proteins in the periplasm and those destined for the outer membranes of Gram-negative bacteria. SurA and Skp are two major periplasmic chaperones, with Skp being the most critical in pathogenic Neisseria since its deletion resulted in drastically reduced levels of the porins PorA and PorB and the surface lipoprotein TbpB. Much of what is known about Skp originates from studies in E. coli, where it was observed as a trimer. In our structural studies, however, Skp from N. meningitidis is a hexamer consisting of a dimer of closely packed interdigitated trimers. Constricted and expanded conformations are observed, indicating the arms of the hexamer are flexible and dynamic. We postulate that Skp in Neisseria must utilize a different mechanism than in E. coli to stabilize substrates by expanding and contracting along its long axis to accommodate substrates of differing sizes.