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1df8

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[[Image:1df8.gif|left|200px]]
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{{STRUCTURE_1df8| PDB=1df8 | SCENE= }}
{{STRUCTURE_1df8| PDB=1df8 | SCENE= }}
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'''S45A MUTANT OF STREPTAVIDIN IN COMPLEX WITH BIOTIN'''
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===S45A MUTANT OF STREPTAVIDIN IN COMPLEX WITH BIOTIN===
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==Overview==
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The contribution of the Ser45 hydrogen bond to biotin binding activation and equilibrium thermodynamics was investigated by biophysical and X-ray crystallographic studies. The S45A mutant exhibits a 1,700-fold greater dissociation rate and 907-fold lower equilibrium affinity for biotin relative to wild-type streptavidin at 37 degrees C, indicating a crucial role in binding energetics. The crystal structure of the biotin-bound mutant reveals only small changes from the wild-type bound structure, and the remaining hydrogen bonds to biotin retain approximately the same lengths. No additional water molecules are observed to replace the missing hydroxyl, in contrast to the previously studied D128A mutant. The equilibrium deltaG degrees, deltaH degrees, deltaS degrees, deltaC degrees(p), and activation deltaG++ of S45A at 37 degrees C are 13.7+/-0.1 kcal/mol, -21.1+/-0.5 kcal/mol, -23.7+/-1.8 cal/mol K, -223+/-12 cal/mol K, and 20.0+/-2.5 kcal/mol, respectively. Eyring analysis of the large temperature dependence of the S45A off-rate resolves the deltaH++ and deltaS++ of dissociation, 25.8+/-1.2 kcal/mol and 18.7+/-4.3 cal/mol K. The large increases of deltaH++ and deltaS++ in the mutant, relative to wild-type, indicate that Ser45 could form a hydrogen bond with biotin in the wild-type dissociation transition state, enthalpically stabilizing it, and constraining the transition state entropically. The postulated existence of a Ser45-mediated hydrogen bond in the wild-type streptavidin transition state is consistent with potential of mean force simulations of the dissociation pathway and with molecular dynamics simulations of biotin pullout, where Ser45 is seen to form a hydrogen bond with the ureido oxygen as biotin slips past this residue after breaking the native hydrogen bonds.
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(as it appears on PubMed at http://www.pubmed.gov), where 10850797 is the PubMed ID number.
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{{ABSTRACT_PUBMED_10850797}}
==About this Structure==
==About this Structure==
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[[Category: Biotin]]
[[Category: Biotin]]
[[Category: Biotin binding protein]]
[[Category: Biotin binding protein]]
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 13:47:03 2008''
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jun 30 22:58:18 2008''

Revision as of 19:58, 30 June 2008

Image:1df8.png

Template:STRUCTURE 1df8

S45A MUTANT OF STREPTAVIDIN IN COMPLEX WITH BIOTIN

Template:ABSTRACT PUBMED 10850797

About this Structure

1DF8 is a Single protein structure of sequence from Streptomyces avidinii. Full crystallographic information is available from OCA.

Reference

Ser45 plays an important role in managing both the equilibrium and transition state energetics of the streptavidin-biotin system., Hyre DE, Le Trong I, Freitag S, Stenkamp RE, Stayton PS, Protein Sci. 2000 May;9(5):878-85. PMID:10850797

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