Abstract
Stomatins belong to the band-7 protein family, a diverse group of conserved eukaryotic and prokaryotic membrane proteins involved in the formation of large protein complexes as protein-lipid scaffolds. The Arabidopsis (Arabidopsis thaliana) genome contains two paralogous genes encoding stomatin-like proteins (SLPs; AtSLP1 and AtSLP2) that are phylogenetically related to human SLP2, a protein involved in mitochondrial fusion and protein complex formation in the mitochondrial inner membrane. We used reverse genetics in combination with biochemical methods to investigate the function of AtSLPs. We demonstrate that both SLPs localize to mitochondrial membranes. SLP1 migrates as a large (approximately 3 MDa) complex in blue-native gel electrophoresis. Remarkably, slp1 knockout mutants have reduced protein and activity levels of complex I and supercomplexes, indicating that SLP affects the assembly and/or stability of these complexes. These findings point to a role for SLP1 in the organization of respiratory supercomplexes in Arabidopsis.
Highlights
Stomatins belong to the band-7 protein family, a diverse group of conserved eukaryotic and prokaryotic membrane proteins involved in the formation of large protein complexes as protein-lipid scaffolds
We have demonstrated that SLP1 localizes to mitochondrial membranes and probably has domains facing both sides of the inner membrane (Fig. 2; Supplemental Fig. S4)
The identification of a processing cleavage site strongly suggests that SLP1 are imported initially into the matrix and processed, and subsequently inserted into the inner membrane via the hydrophobic stretch (Supplemental Fig. S3A)
Summary
Stomatins belong to the band-7 protein family, a diverse group of conserved eukaryotic and prokaryotic membrane proteins involved in the formation of large protein complexes as protein-lipid scaffolds. Two stomatin-like proteins (SLPs) from Arabidopsis (designated as AtSLP1 and AtSLP2) have been identified in several organellar proteomics studies, mainly of the mitochondrial proteome and plant membrane microdomains (Heazlewood et al, 2004; Borner et al, 2005; Dunkley et al, 2006; Mitra et al, 2007). Our results demonstrate mitochondrial membrane localization of AtSLPs and reveal a role in respiratory complex and supercomplex organization that could have implications for the study of band-7 proteins in other species
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