Allosteric regulation of type I hexokinase: A site-directed mutational study indicating location of the functional glucose 6-phosphate binding site in the N-terminal half of the enzyme

Journal Article

The Type I isozyme of mammalian hexokinase has evolved by a gene duplication-fusion mechanism, with resulting internal duplication of sequence and ligand binding sites. However, 1:1 binding stoichiometry indicates that only one of these is available for binding the product inhibitor, Glc-6-P; the location of that site, in the N- or C-terminal half, remains under debate. Recent structural studies (Aleshin et al., Structure 6, 39-50, 1998; Mulichak et al., Nature Struct. Biol. 5, 555-560, 1998) implicated Asp 84 or its analog in the C-terminal half, Asp 532, in binding of Glc-6-P. Zeng et al. (Biochemistry 35, 13157-13164, 1996) demonstrated that mutation of Asp 532 to Lys or Glu did not affect inhibition by the Glc-6-P analog, 1,5- anhydroglucitol-6-P. These same mutations, as well as mutation to Ala, at the Asp 84 position are now shown to result in increased K(i) for 1,5- anhydroglucitol-6-P. The ability of P(i) to antagonize inhibition by the Glc- 6-P analog is severely diminished or abolished by these mutations, suggesting that antagonism is dependent on precise positioning of the inhibitory hexose 6-phosphate. The structure of the enzyme complexed with Glc and P(i) has been determined, and shows that P(i) occupies the same site as the 6-phosphate group in the complex with Glc-6-P. Thus, antagonism between these ligands results from competition for a common anion binding site in the N-terminal half.

Full Text

Duke Authors

Cited Authors

  • Sebastian, S; Wilson, JE; Mulichak, A; Garavito, RM

Published Date

  • 1999

Published In

Volume / Issue

  • 362 / 2

Start / End Page

  • 203 - 210

PubMed ID

  • 9989928

International Standard Serial Number (ISSN)

  • 0003-9861

Digital Object Identifier (DOI)

  • 10.1006/abbi.1998.1043