1u2u
From Proteopedia
|
Nmr solution structure of a designed heterodimeric leucine zipper
Overview
The pH-dependent stability of a protein is strongly affected by, electrostatic interactions between ionizable residues in the folded as, well as unfolded state. Here we characterize the individual contributions, of charged Glu and His residues to stability and determine the NMR, structure of the designed, heterodimeric leucine zipper AB consisting of, an acidic A chain and a basic B chain. Thermodynamic parameters are, compared with those of the homologous leucine zipper AB(SS) in which the A, and B chains are disulfide-linked. NMR structures of AB based on (1)H NMR, data collected at 600 MHz converge, and formation of the same six, interchain salt bridges found previously in disulfide-linked AB(SS), [Marti, D. N., and Bosshard, H. R. (2003) J. Mol. Biol. 330, 621-637] is, indicated. While the structures of AB and AB(SS) are very similar, their, pH-dependent relative stabilities are strikingly different. The stability, of AB peaks at pH approximately 4.5 and is higher at pH 8 than at pH 2. In, contrast, AB(SS) is most stable at acidic pH where no interhelical salt, bridges are formed. The different energetic contributions of charged Glu, and His residues to stability of the two coiled coil structures were, evaluated from pK(a) shifts induced by folding. The six charged Glu, residues involved in salt bridges stabilize leucine zipper AB by 4.5, kJ/mol yet destabilize disulfide-linked AB(SS) by -1.1 kJ/mol. Two, non-ion-paired Glu charges destabilize AB by only -1.8 kJ/mol but AB(SS), by -5.6 kJ/mol. The higher relative stability of AB at neutral pH is not, caused by more favorable electrostatic interactions in the folded leucine, zipper. It is due mainly to unfavorable electrostatic interactions in the, unfolded A and B chains and may therefore be called an inverse, electrostatic effect. This study illustrates the importance of residual, interactions in the unfolded state and how the energetics of the unfolded, state affect the stability of the folded protein.
About this Structure
1U2U is a Protein complex structure of sequences from [1] with ACE and NH2 as ligands. Full crystallographic information is available from OCA.
Reference
Inverse electrostatic effect: electrostatic repulsion in the unfolded state stabilizes a leucine zipper., Marti DN, Bosshard HR, Biochemistry. 2004 Oct 5;43(39):12436-47. PMID:15449933
Page seeded by OCA on Sun Nov 25 03:13:21 2007
