ساختار و وظیفه حامل های میتوکندری (MCs) – نقش غشایی مارپیچ P و G باقی مانده در مکانیزم دریچه و انتقال

ABSTRACT Structure and function of mitochondrial carriers – Role of the transmembrane helix P and G residues in the gating and transport mechanism

Mitochondrial carriers (MCs) are nuclear-coded membrane proteins that transport a variety of solutes (di- and tri carboxylates, keto acids, amino acids, nucleotides and coenzymes/cofactors) across the inner mitochondrial membrane (see [1], [2] for reviews). Besides providing a link between mitochondrial and other cell compartments, MCs play a role in regulating and maintaining a balance between cytosol and mitochondrial matrix, for example, of the phosphorylation and redox potentials. Some carriers, or one of their isoforms if any, are widely distributed in all or nearly all tissues, whereas others are tissue specific and their limited distribution reflects their importance in special tissues, e.g., for fatty acid biosynthesis or thermogenesis.

MCs are small proteins normally possessing a molecular mass of about 30–34 kDa. A main feature is the presence of three internal repeated sequences [3] which were noted immediately after the first MC, the ADP/ATP carrier, had been sequenced [4]. This striking pattern of repeats was also observed in the subsequent five MCs sequenced, leading to the important conclusion that MCs belong to a single protein family, called the mitochondrial carrier family (MCF). All MCF members of known function exhibit a tripartite structure consisting of three tandemly repeated domains of about 100 amino acids in length.