The novel component Kgd4 recruits the E3 subunit to the mitochondrial α-ketoglutarate dehydrogenase.
Bottom Line: Biochemical analyses demonstrate that this protein plays an evolutionarily conserved role in the organization of mitochondrial α-KGDH complexes of fungi and animals.By binding to both the E1-E2 core and the E3 subunit, Kgd4 acts as a molecular adaptor that is necessary to a form a stable α-KGDH enzyme complex.Our work thus reveals a novel subunit of a key citric acid-cycle enzyme and shows how this large complex is organized.
Affiliation: Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden.Show MeSH
Related in: MedlinePlus
Mentions: What could be the molecular function of Kgd4? Because the catalytic subunits are stable in the absence of Kgd4 (Figure 2C), we set out to analyze the composition of KGDH in Δkgd4 cells on linear sucrose gradients. In lysates from wild-type mitochondria, Kgd1, Kgd2, Lpd1, and Kgd4 comigrated (Figure 3A). Because Kgd4 comigrated quantitatively with the complex, these data support the notion that Kgd4 is a subunit of the KGDH. Lpd1 showed two main peaks, one comigrating with KGDH (gray arrow) and one in the top fractions (white arrow), confirming that a substantial amount of Lpd1 exists in a free form in the matrix (Repetto and Tzagoloff, 1991). When analyzing mitochondrial lysates from the Δkgd4 strain, we observed that Kgd2 migrated exclusively with Kgd1 (gray arrow), that a small pool of Kgd1 was additionally present in the top fractions, and that Lpd1 did not comigrate with Kgd2 but was exclusively recovered in the top fractions of the gradient (Figure 3B, white arrow). This observation indicates that a stable interaction of Lpd1 with Kgd1 and Kgd2 depends on Kgd4.
Affiliation: Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden.