Crystal structure and functional characterization of OmpK36, the osmoporin of Klebsiella pneumoniae
- 1 April 1999
- journal article
- research article
- Published by Elsevier BV in Structure
- Vol. 7 (4), 425-434
- https://doi.org/10.1016/s0969-2126(99)80055-0
Abstract
Background: Porins are channel-forming membrane proteins that confer solute permeability to the outer membrane of Gram-negative bacteria. In Escherichia coli, major nonspecific porins are matrix porin (OmpF) and osmoporin (OmpC), which show high sequence homology. In response to high osmolarity of the medium, OmpC is expressed at the expense of OmpF porin. Here, we study osmoporin of the pathogenic Klebsiella pneumoniae (OmpK36), which shares 87% sequence identity with E. coliOmpC in an attempt to establish why osmoporin is best suited to function at high osmotic pressure. Results: The crystal structure of OmpK36 has been determined to a resolution of 3.2 Å by molecular replacement with the model of OmpF. The structure of OmpK36 closely resembles that of the search model. The homotrimeric structure is composed of three hollow 16-stranded antiparallel β barrels, each delimiting a separate pore. Most insertions and deletions with respect to OmpF are found in the loops that protrude towards the cell exterior. A characteristic ten-residue insertion in loop 4 contributes to the subunit interface. At the pore constriction, the replacement of an alanine by a tyrosine residue does not alter the pore profile of OmpK36 in comparison with OmpF because of the different course of the mainchain. Functionally, as characterized in lipid bilayers and liposomes, OmpK36 resembles OmpC with decreased conductance and increased cation selectivity in comparison with OmpF. Conclusions: The osmoporin structure suggests that not an altered pore size but an increase in charge density is the basis for the distinct physico-chemical properties of this porin that are relevant for its preferential expression at high osmotic strength.Keywords
This publication has 32 references indexed in Scilit:
- Structural and Functional Characterization of OmpF Porin Mutants Selected for Larger Pore SizePublished by Elsevier BV ,1996
- From acids to osmZ: multiple factors influence synthesis of the OmpF and OmpC porins in Escherichia coliMolecular Microbiology, 1996
- Reduced surface: An efficient way to compute molecular surfacesPeptide Science, 1996
- Electrostatics and diffusion of molecules in solution: simulations with the University of Houston Brownian Dynamics programComputer Physics Communications, 1995
- Protein Hydration Observed by X-ray Diffraction: Solvation Properties of Penicillopepsin and Neuraminidase Crystal StructuresJournal of Molecular Biology, 1994
- The CCP4 suite: programs for protein crystallographyActa Crystallographica Section D-Biological Crystallography, 1994
- Electrostatic Properties of Two Porin Channels from Escherichia coliJournal of Molecular Biology, 1994
- The regulatory RNA gene micF is present in several species of Gram‐negative bacteria and is phylogenetically conservedMolecular Microbiology, 1994
- Structure of the membrane channel porin from Rhodopseudomonas blastica at 2.0 Å resolutionProtein Science, 1994
- Molecular architecture and functioning of the outer membrane of Escherichia coli and other gram-negative bacteriaBiochimica et Biophysica Acta (BBA) - Reviews on Biomembranes, 1983