PDBsum entry 1osm

Outer membrane protein

PDB id: 1osm

Contents

Protein chains

342 a.a. *

Ligands

D12 ×9

* Residue conservation analysis

PDB id:

1osm

Name:

Outer membrane protein

Title:

Osmoporin (ompk36) from klebsiella pneumoniae

Structure:

Ompk36. Chain: a, b, c. Synonym: osmoporin. Engineered: yes

Source:

Klebsiella pneumoniae. Organism_taxid: 573. Expressed in: escherichia coli. Expression_system_taxid: 562

Biol. unit:

Homo-Trimer (from PDB file)

Resolution:

3.20Å R-factor: 0.208 R-free: 0.223

Authors:

R.Dutzler,T.Schirmer

Key ref:

R.Dutzler et al. (1999). Crystal structure and functional characterization of OmpK36, the osmoporin of Klebsiella pneumoniae. Structure, 7, 425-434. PubMed id: 10196126 DOI: 10.1016/S0969-2126(99)80055-0

Date:

08-Jan-99 Release date: 26-Jul-99

Protein chains

Q48473  (OMPC_KLEPN) -  Outer membrane porin C from Klebsiella pneumoniae

Seq: 363 a.a.

Struc: 342 a.a.

Enzyme reactions

• Enzyme class: E.C.?

DOI no: 10.1016/S0969-2126(99)80055-0

Structure 7:425-434 (1999)

PubMed id: 10196126

Crystal structure and functional characterization of OmpK36, the osmoporin of Klebsiella pneumoniae.

R.Dutzler, G.Rummel, S.Albertí, S.Hernández-Allés, P.Phale, J.Rosenbusch, V.Benedí, T.Schirmer.

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 A 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 beta 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.

Selected figure(s)

Figure 3.
Figure 3. Cyclic-averaged electron-density map (contoured at 1s) of OmpK36. (a) Stereoview of the OmpK36 pore viewed from the extracellular side. Residues of the arginine cluster are labeled (OmpF numbering convention). The internal loop L3 is seen at the right side of the pore. (b) Stereoview of the extracellular loop L4 (with carbon atoms coloured in yellow), which interacts with loop L1 (carbon atoms coloured in white) of a neighbouring monomer. Figures were generated with the program DINO (Philippsen, 1998; http://www.bioz.unibas.ch/ not, vert, similar-xray/dino).

The above figure is reprinted by permission from Cell Press: Structure (1999, 7, 425-434) copyright 1999.

Figure was selected by an automated process.