Membrane potential-dependent conformational changes in mitochondrially bound hexokinase of brain

Area of Science:

• Biochemistry
• Cell Biology
• Neuroscience

Background:

• Hexokinase (HK) is a key enzyme in glucose metabolism, catalyzing the first step of glycolysis.
• Type I hexokinase (HKI) is found in various tissues, including the brain, and plays a critical role in energy production.
• HKI exhibits complex regulatory mechanisms involving interactions with mitochondria.

Purpose of the Study:

• To investigate the structural and functional consequences of hexokinase binding to mitochondria.
• To elucidate the role of mitochondrial interactions in the regulation of cerebral glucose metabolism.

Main Methods:

• Utilized previously characterized monoclonal antibodies (Mabs) to probe soluble and mitochondrially bound forms of rat brain Type I hexokinase.
• Assessed the impact of mitochondrial binding on enzyme conformation and epitope accessibility.
• Investigated the influence of mitochondrial membrane potential and specific inhibitors (oligomycin, carboxyatractyloside, bongkrekic acid) on Mabs' reactivity.

Main Results:

• Mitochondrial binding affects specific epitopic regions in both N- and C-terminal halves of hexokinase.
• Conformational changes induced by ligand binding (glucose or ATP) are modulated by mitochondrial association.
• Mitochondrial membrane potential and inhibitors selectively alter Mabs' reactivity with epitopes on the mitochondrially bound enzyme.
• A glucose-6-phosphate analog showed differential inhibition of extramitochondrial versus intramitochondrial ATP.

Conclusions:

• Hexokinase-mitochondrial interactions induce significant conformational changes in the enzyme.
• These interactions play a regulatory role in cerebral glucose metabolism by modulating hexokinase activity and localization.
• Understanding these interactions provides insights into brain energy homeostasis.