Document Detail


Pentavalent ions dependency is a conserved property of adenosine kinase from diverse sources: identification of a novel motif implicated in phosphate and magnesium ion binding and substrate inhibition.
MedLine Citation:
PMID:  11900549     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
The catalytic activity of adenosine kinase (AK) from mammalian sources has previously been shown to exhibit a marked dependency upon the presence of pentavalent ions (PVI), such as phosphate (PO4), arsenate, or vanadate. We now show that the activity of AK from diverse sources, including plant, yeast, and protist species, is also markedly enhanced in the presence of PVI. In all cases, PO4 or other PVI exerted their effects primarily by decreasing the Km for adenosine and alleviating the inhibition caused by high concentrations of substrates. These results provide evidence that PVI dependency is a conserved property of AK and perhaps of the PfkB family of carbohydrate kinases which includes AK. On the basis of sequence alignments, we have identified a conserved motif NXXE within the PfkB family. The N and E of this motif make close contacts with Mg2+ and PO4 ions in the crystal structures of AK and bacterial ribokinase (another PfkB member which shows PVI dependency), implicating these residues in their binding. Site-directed mutagenesis of these residues in Chinese hamster AK have resulted in active proteins with greatly altered phosphate stimulation and substrate inhibition characteristics. The N239Q mutation leads to the formation of an active protein whose activity was not stimulated by PO4 or inhibited by high concentrations of adenosine or ATP. The activity of the E242D mutant protein was also not significantly altered in the presence of phosphate. Although PO4 had no effect on the KmAdenosine for this mutant, the KmATP, K(i)Adenosine, and K(i)ATP were significantly decreased. In contrast to these mutations, N239L or E242L mutant proteins showed greatly decreased activity with an altered Mg2+ requirement. These observations support the view that N239 and E242 play an important role in the binding of PO4 and Mg2+ ions required for the catalytic activity of adenosine kinase.
Authors:
Mary C Maj; Bhag Singh; Radhey S Gupta
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Biochemistry     Volume:  41     ISSN:  0006-2960     ISO Abbreviation:  Biochemistry     Publication Date:  2002 Mar 
Date Detail:
Created Date:  2002-03-19     Completed Date:  2002-04-19     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0370623     Medline TA:  Biochemistry     Country:  United States    
Other Details:
Languages:  eng     Pagination:  4059-69     Citation Subset:  IM    
Affiliation:
Department of Biochemistry, McMaster University, Hamilton, Ontario, Canada, L8N 3Z5.
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MeSH Terms
Descriptor/Qualifier:
Adenosine Kinase / antagonists & inhibitors,  chemistry,  genetics,  metabolism*
Amino Acid Motifs*
Amino Acid Sequence
Animals
Anions
CHO Cells
Cations
Cricetinae
DNA, Complementary
Magnesium / metabolism*
Molecular Sequence Data
Mutagenesis, Site-Directed
Phosphates / metabolism*
Sequence Homology, Amino Acid
Substrate Specificity
Chemical
Reg. No./Substance:
0/Anions; 0/Cations; 0/DNA, Complementary; 0/Phosphates; 7439-95-4/Magnesium; EC 2.7.1.20/Adenosine Kinase

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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