The TOB/SAM complex composition in mitochondria of Dictyostelium discoideum during progression from unicellularity to multicellularity

Abstract

Despite its complex life cycle including unicellular and multicellular stages, the slime mold Dictyostelium discoideum, a well-known model in biomedical research, has not been used as a model organism in studies on mitochondrial import, including its significance in cellular processes. Moreover, data concerning mitochondrial protein import machinery in D. discoideum mitochondria is limited and nothing is known about the impact of that machinery on slime mold life cycle. Here, we focused on the TOB/SAM (topogenesis of the mitochondrial outer membrane β-barrel proteins/sorting and assembly machinery) complex. This complex is localized in the mitochondrial outer membrane and is indispensable for the formation of metabolite exchange and protein import pathways in the membrane, and substantially contributes to the regulation of mitochondrial morphology and distribution. Furthermore, the available data suggests that the TOB/SAM complex variants differ between mitochondria of multicellular and unicellular eukaryotes. Therefore, we decided to determine these variants of the TOB/SAM in mitochondria of D. discoideum progressing from single cells to early multicellular stages, when the cells stream together to form a multicellular organism. The results revealed two complex variants of the TOB/SAM complex of about 160 and 600 kDa molecular weight, present in mitochondria of D. discoideum cells at the studied stages. The discussed complex variants resemble the ones that have been already detected for the yeast Saccharomyces cerevisiae, fungus Neurospora crassa and human cells, and one of investigated variants differentiates unicellular and initial multicellular stages of the D. discoideum life cycle.