The molecular structure of mitochondrial contact sites. Their role in regulation of energy metabolism and permeability transition

Abstract

Contact sites between the outer and peripheral inner membrane of mitochondria are involved in protein precursor uptake and energy transfer. Hexokinase and mitochondrial creatine kinase could be attributed by different techniques to the energy transfer contacts. Kinetic analyses suggested a functional interaction between the kinases, outer membrane pore protein, and inner membrane adenylate translocator (ANT). This suggestion was strongly supported by isolation of hexokinase and creatine kinase complexes that were constituted of kinase oligomers, porin and ANT. Phospholipid vesicles carrying reconstituted kinase-porin-ANT complexes enclosed internal ATP in contrast to vesicles containing free porin only. This indicated that unspecific transport through porin was regulated by its interaction with a specific antiporter, ANT. A direct interaction between porin and ANT in the hexokinase complex conferred the reconstituted system with permeability properties reminiscent of the mitochondrial permeability transition (PT) pore. In the creatine kinase complex this interaction between porin and ANT was replaced by contact of both with the kinase octamer. Thus PT-pore-like functions were not observed unless the creatine kinase octamer was dissociated, suggesting that the ANT was locked in the antiporter state by interaction with the octamer. Indeed, reconstituted pure ANT showed PT-pore-like properties concerning Ca2+ sensitivity. However, as cyclophilin was missing, sensitivity against cyclosporin was not observed.

The Human nm23-H4 Gene Product Is a Mitochondrial Nucleoside Diphosphate Kinase

“…More recently, NDP kinase activity was found associated with the contact sites between the outer and the inner membranes (52)(53)(54). In a first attempt to determine the submitochondrial localization of Nm23-H4, we have prepared mitochondrial subfractions of HEK 293 cells.…”

“…These sites were shown to be involved in the transport of proteins, solute, and energy (54). They contain a polyprotein channel, the permeability transition pore, which includes porin (or voltage anion-dependent channel), the ATP/ADP carrier, and kinases, hexokinase, and creatine kinase (52).…”

C-terminal Lysines Determine Phospholipid Interaction of Sarcomeric Mitochondrial Creatine Kinase

“…These facts already point to a specific functional role of the mitochondrial CK octamer. In fact, MtCK is part of proteolipid complexes localized in the cristae and the peripheral intermembrane space of mitochondria (7,8). These proteolipid complexes form microcompartments that maintain a privileged exchange of substrates and products, the so-called functional coupling (see Fig.…”

Mitochondrial calcium handling during ischemia-induced cell death in neurons

“…Despite the great interest generated by this channel, which has been extensively characterized at the pharmacological and biophysical level, the molecular identity of the PTP is not known. The classical model envisions a supramolecular complex spanning the double membrane system of mitochondria, localized at contact sites [78]. Proteins of all mitochondrial compartments have been proposed to be part of the PTP [66,67,79], in particular cyclophilin D (CypD) in the mitochondrial matrix, the adenine nucleotide translocator in the inner membrane and mitochondrial porin VDAC in the outer membrane.…”