1xch
From Proteopedia
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'''MYOGLOBIN (HORSE HEART) MUTANT WITH LEU 104 REPLACED BY ASN (L104N)''' | '''MYOGLOBIN (HORSE HEART) MUTANT WITH LEU 104 REPLACED BY ASN (L104N)''' | ||
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[[Category: Brayer, G D.]] | [[Category: Brayer, G D.]] | ||
[[Category: Maurus, R.]] | [[Category: Maurus, R.]] | ||
| - | [[Category: | + | [[Category: Heme]] |
| - | [[Category: | + | [[Category: Muscle]] |
| - | [[Category: | + | [[Category: Oxygen transport]] |
| - | [[Category: | + | [[Category: Respiratory protein]] |
| - | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 14:51:15 2008'' | |
| - | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on | + | |
Revision as of 11:51, 3 May 2008
MYOGLOBIN (HORSE HEART) MUTANT WITH LEU 104 REPLACED BY ASN (L104N)
Overview
Well-ordered internal amino acids can contribute significantly to the stability of proteins. To investigate the importance of the hydrophobic packing interface between helices G and H in the proximal heme pocket of horse heart myoglobin, the highly conserved amino acid, Leu104, was substituted with asparagine, a polar amino acid of similar size. The Leu104Asn mutant protein and its recombinant wild-type horse heart myoglobin counterpart were expressed from synthetic genes in Escherichia coli. Thermal denaturation of these two recombinant myoglobins, as studied by measurement of circular dichroism ellipticity at 222 nm, revealed that the Leu104Asn mutant had a significantly lower t(m) (71.8 +/- 1 degree C, pH 7.0) than recombinant wild-type myoglobin (81.3 +/- 1 degree C, pH 7.0). To examine the extent to which this 10 degrees C decrease in thermal stability was associated with structural perturbations, X-ray diffraction techniques were used to determine the three-dimensional structures of both the recombinant wild-type and Leu104Asn myoglobins to 0.17 nm resolution. Refinement of these structures gave final crystallographic R-factors of 16.0% and 17.9%, respectively. Structural comparison of the natural and recombinant wild-type myoglobins, together with absorption spectroscopic and electron paramagnetic resonance (EPR) analyses, confirmed the proper expression and folding of the recombinant protein in E. coli. Surprisingly, despite the decreased thermal stability of the Leu104Asn mutant, there are no significant structural differences between the mutant and wild-type myoglobins. EPR and absorption spectroscopic analyses further confirmed the similar nature of the heme iron centres in both proteins. Thus, the introduction of an energetically unfavourable change in side chain polarity at position 104 into a hydrophobic environment that does not support the hydrogen bonding potential of the mutant asparagine appears to perturb important stabilizing helix-helix and heme-protein interactions. The induced structural destabilization is thereby reflected by a significant decrease in the t(m) of horse heart myoglobin.
About this Structure
1XCH is a Single protein structure of sequence from Equus caballus. Full crystallographic information is available from OCA.
Reference
A myoglobin variant with a polar substitution in a conserved hydrophobic cluster in the heme binding pocket., Maurus R, Overall CM, Bogumil R, Luo Y, Mauk AG, Smith M, Brayer GD, Biochim Biophys Acta. 1997 Aug 15;1341(1):1-13. PMID:9300804 Page seeded by OCA on Sat May 3 14:51:15 2008
