May 2004
Volume 45, Issue 13
Free
ARVO Annual Meeting Abstract  |   May 2004
The RanBP2 Associates with two Novel Mitochondrial Components, Hexokinase and Cox11, and Modulates the Activity of Hexokinase
Author Affiliations & Notes
  • R. Bhowmick
    Pharmacology & Toxicology, Medical College of Wisconsin, Milwaukee, WI
  • A. Aslanukov
    Pharmacology & Toxicology, Medical College of Wisconsin, Milwaukee, WI
  • P.A. Ferreira
    Pharmacology & Toxicology, Medical College of Wisconsin, Milwaukee, WI
  • Footnotes
    Commercial Relationships  R. Bhowmick, None; A. Aslanukov, None; P.A. Ferreira, None.
  • Footnotes
    Support  EY1993/EY12655
Investigative Ophthalmology & Visual Science May 2004, Vol.45, 669. doi:
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      R. Bhowmick, A. Aslanukov, P.A. Ferreira; The RanBP2 Associates with two Novel Mitochondrial Components, Hexokinase and Cox11, and Modulates the Activity of Hexokinase . Invest. Ophthalmol. Vis. Sci. 2004;45(13):669.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Abstract: : Purpose: The RanBP2 is an unique vertebrate protein highly expressed in the retina and comprised of multiple, unrelated and related structural modules. We identified previously several proteins that associate specifically with selective domains of RanBP2. However, the role of Leucine–rich domain (LD) of RanBP2 is still unknown. The goal of this work was to identify molecular partners with specific binding activity towards the LD of RanBP2, to carry out detailed structure–function analysis of LD and to determine the LD effect(s) on its molecular partners. Methods: We carried out a combination biochemical binding assays of GST–fused LD constructs with retinal extracts and two independent yeast two–hybrid screens of 18 million clones derived from murine adult and embryonic brain libraries to identify molecular partners of LD of RanBP2. Results: Two novel molecular partners, hexokinase (HK) and Cox11, were identified. The former is the "pacemaker" of glycolysis, while the latter is a metallochaperone implicated in the assembly of cytochrome c oxidase. The leucine zipper motif of LD of RanBP2 confers the binding activity of LD towards HK. In contrast, Cox11 requires the complete LD of RanBP2 for optimal interaction. The intermembrane mitochondrial domain of Cox11 retains most of the binding activity towards LD of RanBP2. In vitro reconstitution assays showed that RanBP2 exhibits strong affinity towards a folding intermediate of the monomeric apoprotein and the mature metalloprotein chaperone. In addition, enzymatic assays support the LD of RanBP2 markedly decreases HK activity likely by a reduction of its Vmax. Conclusion: These studies support a role of RanBP2 in the biogenesis of mitochondrial components. In addition, allosteric modulation of HK activity by RanBP2 is achieved by the sequestration of HK to the LD of RanBP2. In light of the excessive amount of HK in the CNS and the low buffering capacity of the CNS for glucose, the RanBP2 emerges as a central regulatory component in coupling the glycolytic and oxidative phases of glucose metabolism. RanBP2 deficient mice will serve to test and explore this model.

Keywords: retina • protein structure/function • chaperones 
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