The structure of mitochondrial creatine kinase and its membrane binding properties

Abstract

The biochemical and biophysical characterization of the mitochondrial creatine kinase (Mi-CK) from chicken cardiac muscle is reviewed with emphasis on the structure of the octameric oligomer by electron microscopy and on its membrane binding properties. Information about shape, molecular symmetry and dimensions of the Mi-CK octamer, as obtained by different sample preparation techniques in combination with image processing methods, are compared. The organization of the four dimeric subunits into the Mi-CK complex as apparent as apparent in the end-on projections is discussed and the consistently observed high binding affinity of the four-fold symmetric end-on faces towards many support films and towards each other is outlined. A study on the oligomeric state of the enzyme in solution and in intact mitochondria, using chemical crosslinking reagents, is presented together with the results of a search for a possible linkage of Mi-CK with the adenine nucleotide translocator (ANT). The nature of Mi-CK binding to model membranes, demonstrating that rather the octameric than the dimeric subspecies is involved in lipid interaction and membrane contact formation, is resumed and put into relation to our structural observations. The findings are discussed in light of a possible in vivo function of the Mi-CK octamer bridging the gap between outer and inner mitochondrial membranes at the contact sites.

Mitochondrial Creatine Kinase and Mitochondrial Outer Membrane Porin Show a Direct Interaction That Is Modulated by Calcium

“…3 and 34) and to allow co-purification of ANT⅐MtCK⅐porin complexes (11). For interaction of MtCK with porin in the outer membrane, which is almost deficient of cardiolipin, a similar indirect complex formation via other charged phospholipids has been proposed (9). However, our present data clearly show that, in contrast to ANT, porin can directly interact with MtCK.…”

“…Other binding partners have been ruled out so far on the basis of cross-linking studies (9,10). Now, in addition to phospholipids, porin can be classed as a new binding partner for MtCK in the outer mitochondrial membrane.…”

“…Chemical cross-linking of contact site proteins has failed so far (9,10). Co-purification of MtCK, ANT, and porin in proteolipid contact site complexes only indicated a close proximity of these proteins (11).…”

Maturation of Cardiac Energy Metabolism During Perinatal Development

“…This enzyme, responsible for the reversible transfer of the high energy bound of ATP to creatine (Cr) (ATP + Cr ↔ ADP + PCr) is at the heart of a system of energy transfer that is based on a complex organization of the different isoforms of CK ( Figure 2 ). Cytosolic CK [predominantly represented by the MM-CK isoenzyme in the heart ( Wallimann et al, 1992 )] is either free in the cytoplasm or bound near ATPases of myofilaments and sarcoplasmic reticulum ( Wallimann and Eppenberger, 1985 ; Rossi et al, 1990 ), whereas mitochondrial CK (mi-CK) is located in the mitochondrial intermembrane space near the adenine nucleotide translocase (ANT) (for reviews, see Saks et al, 1977 ; Wallimann et al, 1992 ; Schnyder et al, 1994 ). Insofar as ANT ensures the importation of ADP into the mitochondrial matrix and the export of the newly synthesized ATP to the intermembrane space ( Saks et al, 1994 ), it supplies the mi-CK with ATP which can then produce PCr in the vicinity of the mitochondria.…”

Enzymatic Characteristics of Creatine Kinase System under Conditions of Cerebral Circulatory Disorders

“…Activity of mCK is mainly determined by the interaction with the mitochondrial membrane [12]. mCK exists in two oligomeric forms (octamer and dimer) that are capable of undergoing mutual transitions [10]. cCK is pre sent in the cell only as a dimer.…”