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J. Biol. Chem., Vol. 275, Issue 21, 15773-15781, May 26, 2000
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From the Department of Biochemistry, Kansas State University,
Manhattan, Kansas 66506
Pyruvate dehydrogenase kinase (PDK) isoforms 2 and 3 were produced via co-expression with the chaperonins GroEL and
GroES and purified with high specific activities in affinity tag-free forms. By using human components, we have evaluated how binding to the
lipoyl domains of the dihydrolipoyl acetyltransferase (E2) produces the
predominant changes in the rates of phosphorylation of the pyruvate
dehydrogenase (E1) component by PDK2 and PDK3. E2 assembles as a 60-mer
via its C-terminal domain and has mobile connections to an E1-binding
domain and then two lipoyl domains, L2 and L1 at the N terminus. PDK3
was activated 17-fold by E2; the majority of this activation was
facilitated by the free L2 domain (half-maximal activation at 3.3 µM L2). The direct activation of PDK3 by the L2
domain resulted in a 12.8-fold increase in kcat along with about a 2-fold decrease in the Km of
PDK3 for E1. PDK3 was poorly inhibited by pyruvate or dichloroacetate (DCA). PDK3 activity was stimulated upon reductive acetylation of L1
and L2 when full activation of PDK3 by E2 was avoided (e.g. using free lipoyl domains or ADP-inhibited E2-activated PDK3). In
marked contrast, PDK2 was not responsive to free lipoyl domains, but
the E2-60-mer enhanced PDK2 activity by 10-fold. E2 activation of PDK2
resulted in a greatly enhanced sensitivity to inhibition by pyruvate or
DCA; pyruvate was effective at significantly lower levels than DCA.
E2-activated PDK2 activity was stimulated
Marked Differences between Two Isoforms of Human Pyruvate
Dehydrogenase Kinase*
3-fold by reductive
acetylation of E2; stimulated PDK2 retained high sensitivity to
inhibition by ADP and DCA. Thus, PDK3 is directly activated by the L2
domain, and fully activated PDK3 is relatively insensitive to
feed-forward (pyruvate) and feed-back (acetylating) effectors. PDK2 was
activated only by assembled E2, and this activated state beget high
responsiveness to those effectors.
*
This work was supported by National Institutes of Health
Grant DK18320 and by the Kansas Agriculture Experiment Station
Contribution 00-189-J.The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
To whom correspondence should be addressed: Dept. of Biochemistry,
104 Willard Hall, Kansas State University, Manhattan, KS 66506. Tel.:
785-532-6116; Fax: 785-532-7278.
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