160l: Difference between revisions
No edit summary |
No edit summary |
||
| Line 1: | Line 1: | ||
[[Image:160l.jpg|left|200px]] | [[Image:160l.jpg|left|200px]] | ||
<!-- | |||
The line below this paragraph, containing "STRUCTURE_160l", creates the "Structure Box" on the page. | |||
You may change the PDB parameter (which sets the PDB file loaded into the applet) | |||
or the SCENE parameter (which sets the initial scene displayed when the page is loaded), | |||
or leave the SCENE parameter empty for the default display. | |||
| | --> | ||
| | {{STRUCTURE_160l| PDB=160l | SCENE= }} | ||
}} | |||
'''CONTROL OF ENZYME ACTIVITY BY AN ENGINEERED DISULFIDE BOND''' | '''CONTROL OF ENZYME ACTIVITY BY AN ENGINEERED DISULFIDE BOND''' | ||
| Line 28: | Line 25: | ||
[[Category: Blaber, M.]] | [[Category: Blaber, M.]] | ||
[[Category: Matthews, B W.]] | [[Category: Matthews, B W.]] | ||
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 09:31:52 2008'' | |||
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on | |||
Revision as of 09:31, 2 May 2008
CONTROL OF ENZYME ACTIVITY BY AN ENGINEERED DISULFIDE BOND
OverviewOverview
A series of individual alanine mutations has been constructed in the helical region 115 to 123 in phage T4 lysozyme in order to evaluate the contribution to protein stability of the different side-chains within this region. Pairwise alanine mutations and a combination mutant with seven alanine substitutions were constructed to evaluate the additive effects upon structure and stability. Only three residues within this region (Ser117, Leu118 and Leu121) have a substantial influence upon stability (change in free energy of unfolding greater than 1.0 kcal/mol). Replacement of Ser117 with alanine results in an increase in protein stability of 1.27 kcal/mol, apparently due to the release of strain present in the wild-type protein. Replacement of the buried residues Leu118 and Leu121 is destabilizing. Substitution of the remaining six residues with alanine has relatively little effect on stability. This is consistent with prior studies showing that only 20 to 30% of the residues in amphipathic helices in T4 lysozyme are critical for stability. For some of the pairwise alanine mutants the effects on stability are additive. For most of these mutants, however, there is a slight (approximately 0.15 to 0.25 kcal/mol) non-additivity such that the double mutant is more stable than the sum of the constituent single mutants. This effect is consistently observed for residues with positions i, i +4; i.e. adjacent, but in consecutive turns of the helix, suggesting a weak but significant interaction between these amino acid residues. A more pronounced non-additivity (approximately 0.5 kcal/mol) is seen in the seven-alanine combination mutant. This non-additivity is due to a modest "collapse" or "repacking" that occurs for the combination mutants (especially the multiple alanine mutant) but is not possible for the single replacements. The truncation of some side-chains permits an increase in solvent accessibility of main-chain amide and carbonyl groups. This effect is most pronounced for the seven-alanine combination mutant, where two solvent molecules, not present in wild-type, hydrogen bond to main-chain carbonyl groups in the middle region of the helix. It has been suggested that the binding of such water molecules might represent the first step in solvent-mediated unfolding of an alpha-helix. The appearance of ordered solvent, however, appears to have very little effect on stability (approximately less than 0.2 kcal/mol).
About this StructureAbout this Structure
160L is a Single protein structure of sequence from Enterobacteria phage t4. Full crystallographic information is available from OCA.
ReferenceReference
Alanine scanning mutagenesis of the alpha-helix 115-123 of phage T4 lysozyme: effects on structure, stability and the binding of solvent., Blaber M, Baase WA, Gassner N, Matthews BW, J Mol Biol. 1995 Feb 17;246(2):317-30. PMID:7869383 Page seeded by OCA on Fri May 2 09:31:52 2008