Document Detail

Insensitivity of perturbed carboxyl pK(a) values in the ovomucoid third domain to charge replacement at a neighboring residue.
MedLine Citation:
PMID:  10891089     Owner:  NLM     Status:  MEDLINE    
A number of carboxyl groups in turkey ovomucoid third domain (OMTKY3) have low pK(a) values. A previous study suggested that neighboring amino groups were primarily responsible for the low carboxyl pK(a) values. However, the expected elevation in pK(a) values for these amino groups was not observed. In the present study, site-directed mutagenesis is used to investigate the origins of perturbed carboxyl pK(a) values in OMTKY3. Electrostatic calculations suggest that Lys 34 has large effects, 0.4-0.6 unit, on Asp 7, Glu 10, and Glu 19 which are 5-11 A away from Lys 34. Two-dimensional (1)H NMR techniques were used to determine pK(a) values of the acidic residues in OMTKY3 mutants in which Lys 34 has been replaced with threonine and glutamine. Surprisingly, the pK(a) values in the mutants are very close to those of the wild-type protein. The insensitivity of the acidic residues to replacement of Lys 34 suggests that long-range electrostatic interactions play less of a role in perturbing carboxyl pK(a) values than originally thought. We hypothesize that hydrogen bonds play a key role in perturbing some of the carboxyl ionization equilibria in OMTKY3.
W R Forsyth; A D Robertson
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Biochemistry     Volume:  39     ISSN:  0006-2960     ISO Abbreviation:  Biochemistry     Publication Date:  2000 Jul 
Date Detail:
Created Date:  2000-08-04     Completed Date:  2000-08-04     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  0370623     Medline TA:  Biochemistry     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  8067-72     Citation Subset:  IM    
Department of Biochemistry, University of Iowa, Iowa City, Iowa 52242, USA.
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MeSH Terms
Amides / chemistry
Hydrogen-Ion Concentration
Magnetic Resonance Spectroscopy
Models, Molecular
Mutagenesis, Site-Directed
Ovomucin / chemistry*,  genetics
Recombinant Proteins / chemistry
Grant Support
Reg. No./Substance:
0/Amides; 0/Recombinant Proteins; 37281-36-0/Ovomucin

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