1qhe: Difference between revisions
New page: left|200px<br /><applet load="1qhe" size="450" color="white" frame="true" align="right" spinBox="true" caption="1qhe, resolution 2.0Å" /> '''ENERGETICS OF A HYDRO... |
No edit summary |
||
| Line 1: | Line 1: | ||
[[Image:1qhe.jpg|left|200px]]<br /><applet load="1qhe" size=" | [[Image:1qhe.jpg|left|200px]]<br /><applet load="1qhe" size="350" color="white" frame="true" align="right" spinBox="true" | ||
caption="1qhe, resolution 2.0Å" /> | caption="1qhe, resolution 2.0Å" /> | ||
'''ENERGETICS OF A HYDROGEN BOND (CHARGED AND NEUTRAL) AND OF A CATION-PI INTERACTION IN APOFLAVODOXIN'''<br /> | '''ENERGETICS OF A HYDROGEN BOND (CHARGED AND NEUTRAL) AND OF A CATION-PI INTERACTION IN APOFLAVODOXIN'''<br /> | ||
==Overview== | ==Overview== | ||
Anabaena apoflavodoxin contains a single histidine residue (H34) that | Anabaena apoflavodoxin contains a single histidine residue (H34) that interacts with two aromatic residues (F7 and Y47). The histidine and phenylalanine rings are almost coplanar and they can establish a cation-pi interaction when the histidine is protonated. The histidine and tyrosine side-chains are engaged in a hydrogen bond, which is their only contact. We analyse the energetics of these interactions using p Ka-shift analysis, double-mutant cycle analysis at two pH values, and X-ray crystallography. The H/F interaction is very weak when the histidine is neutral, but it is strengthened by 0.5 kcal mol-1on histidine protonation. Supporting this fact, the histidine p Kain a F7L mutant is 0.4 pH units lower than in wild-type. The strength of the H/Y hydrogen bond is 0.7 kcal mol-1when the histidine is charged, and it becomes stronger (1.3 kcal mol-1) when the histidine is neutral. This is consistent with our observation that the (H34)Nepsilon2-OH(Y47) distance is slightly shorter in the apoflavodoxin structure at pH 9.0 than in the previously reported structure at pH 6.0. It is also consistent with a histidine p Kavalue 0.6 pH units higher in a Y47F mutant than in the wild-type protein. We suggest that the higher stability of the neutral hydrogen bond could be due to a higher desolvation penalty of the charged hydrogen bond that would offset its more favourable enthalpy of formation. The relationship between hydrogen bond strength and the contribution of hydrogen bonds to protein stability is discussed. | ||
==About this Structure== | ==About this Structure== | ||
1QHE is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Anabaena_sp. Anabaena sp.] with SO4 as [http://en.wikipedia.org/wiki/ligand ligand]. Full crystallographic information is available from [http:// | 1QHE is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Anabaena_sp. Anabaena sp.] with <scene name='pdbligand=SO4:'>SO4</scene> as [http://en.wikipedia.org/wiki/ligand ligand]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1QHE OCA]. | ||
==Reference== | ==Reference== | ||
| Line 19: | Line 19: | ||
[[Category: flavodoxin]] | [[Category: flavodoxin]] | ||
''Page seeded by [http:// | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 14:39:35 2008'' | ||
Revision as of 15:39, 21 February 2008
|
ENERGETICS OF A HYDROGEN BOND (CHARGED AND NEUTRAL) AND OF A CATION-PI INTERACTION IN APOFLAVODOXIN
OverviewOverview
Anabaena apoflavodoxin contains a single histidine residue (H34) that interacts with two aromatic residues (F7 and Y47). The histidine and phenylalanine rings are almost coplanar and they can establish a cation-pi interaction when the histidine is protonated. The histidine and tyrosine side-chains are engaged in a hydrogen bond, which is their only contact. We analyse the energetics of these interactions using p Ka-shift analysis, double-mutant cycle analysis at two pH values, and X-ray crystallography. The H/F interaction is very weak when the histidine is neutral, but it is strengthened by 0.5 kcal mol-1on histidine protonation. Supporting this fact, the histidine p Kain a F7L mutant is 0.4 pH units lower than in wild-type. The strength of the H/Y hydrogen bond is 0.7 kcal mol-1when the histidine is charged, and it becomes stronger (1.3 kcal mol-1) when the histidine is neutral. This is consistent with our observation that the (H34)Nepsilon2-OH(Y47) distance is slightly shorter in the apoflavodoxin structure at pH 9.0 than in the previously reported structure at pH 6.0. It is also consistent with a histidine p Kavalue 0.6 pH units higher in a Y47F mutant than in the wild-type protein. We suggest that the higher stability of the neutral hydrogen bond could be due to a higher desolvation penalty of the charged hydrogen bond that would offset its more favourable enthalpy of formation. The relationship between hydrogen bond strength and the contribution of hydrogen bonds to protein stability is discussed.
About this StructureAbout this Structure
1QHE is a Single protein structure of sequence from Anabaena sp. with as ligand. Full crystallographic information is available from OCA.
ReferenceReference
Energetics of a hydrogen bond (charged and neutral) and of a cation-pi interaction in apoflavodoxin., Fernandez-Recio J, Romero A, Sancho J, J Mol Biol. 1999 Jul 2;290(1):319-30. PMID:10388575
Page seeded by OCA on Thu Feb 21 14:39:35 2008