Reversal of ADP-mediated aggregation of adenosine kinase by cyclophilin leads to its reactivation
Metadata of CSIR Papers
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| Title |
Reversal of ADP-mediated aggregation of adenosine kinase by cyclophilin leads to its reactivation
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| Creator |
Sen, B
Chakraborty, A Datta, R Bhattacharyya, D Datta, AK |
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| Subject |
Biochemistry & Molecular Biology
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| Description |
Cyclophilins have been implicated in several important cellular functions. Our earlier results showed that reactivation of adenosine kinase (AdK) by CyP (LdCyP) from the parasitic protozoa Leishmania donovani is accompanied with disaggregation of the enzyme [Chakraborty, A., et al. (2002) J. Biol. Chem. 277, 47451-47460; Chakraborty, A., et al. (2004) Biochemistry 43, 11862-11872]. However, it remained to be known why the enzyme displayed progressive inhibition during the time-dependent reaction and what LdCyP does to prevent and/or reverse the inhibition. Herein, we demonstrate that one of its reaction products,. ADP but not AMP, facilitates the formation of AdK aggregates, leading to its inactivation. Further studies revealed that LdCyP reactivates the enzyme by withdrawing the ADP inhibition. To investigate the molecular mechanism, the intrinsic tryptophan fluorescence and polarization of AdK were monitored in the presence of either LdCyP or ADP and in combination thereof. Whereas in the presence of LdCyP the tryptophan fluorescence emission maxima of AdK exhibited a red shift, ADP had a quenching effect. However, both the red shift and quenching became less noticeable when one (W234) of the two tryptophan residues of AdK was altered, indicating W234 fluorescence is relatively more sensitive to both LdCyP and ADP binding. Kinetic measurements indicated that LdCyP-facilitated reactivation of AdK is accompanied with a concomitant increase in the K-D of ADP but not of AMP. Interestingly, addition of myokinase (MK) and pyruvate kinase (PK) along with phosphoenolpyruvate, either singly or in conjunction, to the AdK reaction mixture led to its reactivation. The effect of PK but not of MK could be substituted by CyP and vice versa. Taken together, the results suggest that LdCyP-induced reactivation occurs due to conformational reorientation of AdK in a manner that decreases the affinity of the enzyme for ADP with consequent relief from the ADP-mediated aggregation.
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| Publisher |
AMER CHEMICAL SOCWASHINGTON1155 16TH ST, NW, WASHINGTON, DC 20036 USA
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| Date |
2011-09-20T12:12:21Z
2011-09-20T12:12:21Z 2006 |
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| Type |
Article
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| Identifier |
BIOCHEMISTRY
0006-2960 http://hdl.handle.net/123456789/14240 |
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| Language |
English
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