1bt9
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(New page: 200px<br /><applet load="1bt9" size="450" color="white" frame="true" align="right" spinBox="true" caption="1bt9, resolution 3.0Å" /> '''OMPF PORIN MUTANT D74...)
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Revision as of 09:47, 20 November 2007
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OMPF PORIN MUTANT D74A
Overview
The channel-forming protein OmpF porin from Escherichia coli spans the, bacterial outer membrane. Each of the three monomers comprises a hollow, 16-stranded beta-barrel. These are associated to homotrimers which are, unusually stable, due mostly to hydrophobic interactions between the, beta-barrels. In addition, a loop, L2 connects one subunit to its neighbor, by latching into its channel. Residue E71 on loop 2 is integrated into an, ionic network and forms salt bridges and hydrogen bonds with R100 and R132, on the channel wall in the adjacent subunit. To examine these, contributions quantitatively, six single-site, two double, and one, deletion mutant were constructed on the basis of the atomic coordinates of, the protein. Differential scanning calorimetric analysis showed that the, salt-bridge, E71-R100, contributes significantly to trimer stability: the, substitution E71Q causes a decrease of the transition temperature from 72, to 48 degreesC, with DeltaHcal diminishing from 430 to 201 kcal mol-1. A, nearby substitution in the loop, D74N, has lesser effects on thermal, stability, while the deletion in L2 (Delta69-77) has an effect comparable, to that of E71Q. X-ray structure analysis to 3.0 A resolution revealed, only local structural differences in the mutants except for the, substitution R100A, where another residue, R132, is found to fill the gap, left by the truncated side chain of A100. Functional assays in planar, lipid bilayers show significantly increased cation selectivities if the, charge distribution was affected.
About this Structure
1BT9 is a Single protein structure of sequence from Escherichia coli. Full crystallographic information is available from OCA.
Reference
Stability of trimeric OmpF porin: the contributions of the latching loop L2., Phale PS, Philippsen A, Kiefhaber T, Koebnik R, Phale VP, Schirmer T, Rosenbusch JP, Biochemistry. 1998 Nov 10;37(45):15663-70. PMID:9843370
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