Structural organization of mitochondrial human complex I: role of the ND4 and ND5 mitochondria-encoded subunits and interaction with prohibitin

Abstract

Mitochondria-encoded ND (NADH dehydrogenase) subunits, as components of the hydrophobic part of complex I, are essential for NADH:ubiquinone oxidoreductase activity. Mutations or lack of expression of these subunits have significant pathogenic consequences in humans. However, the way these events affect complex I assembly is poorly documented. To understand the effects of particular mutations in ND subunits on complex I assembly, we studied four human cell lines: ND4 non-expressing cells, ND5 non-expressing cells, and rho degrees cells that do not express any ND subunits, in comparison with normal complex I control cells. In control cells, all the seven analysed nuclear-encoded complex I subunits were found to be attached to the mitochondrial inner membrane, except for the 24 kDa subunit, which was nearly equally partitioned between the membranes and the matrix. Absence of a single ND subunit, or even all the seven ND subunits, caused no major changes in the nuclear-encoded complex I subunit content of mitochondria. However, in cells lacking ND4 or ND5, very low amounts of 24 kDa subunit were found associated with the membranes, whereas most of the other nuclear-encoded subunits remained attached. In contrast, membrane association of most of the nuclear subunits was significantly reduced in the absence of all seven ND proteins. Immunopurification detected several subcomplexes. One of these, containing the 23, 30 and 49 kDa subunits, also contained prohibitin. This is the first description of prohibitin interaction with complex I subunits and suggests that this protein might play a role in the assembly or degradation of mitochondrial complex I.

Proteomics analysis of mitochondrial proteins reveals overexpression of a mitochondrial protein chaperon, prohibitin, in cells expressing hepatitis C virus core protein

“…In addition, there are several studies that showed the association of prohibitin with the assembly of mitochondrial respiratory complex I as well as complex IV (COX). 21,28 Complex I also consists of both nuclear-and mitochondrial-DNA-encoded subunits; therefore, it is probable that the assembly and function of complex I are impaired by the core protein. We attempted to examine the interaction of prohibitin with the mitochondrial DNA-encoded subunit of complex I, but commercially available antibodies against this subunit could not detect the protein itself by immunoblotting (data not shown).…”

Identification of Mitochondrial Complex I Assembly Intermediates by Tracing Tagged NDUFS3 Demonstrates the Entry Point of Mitochondrial Subunits

“…For example, in Chlamydomonas CI, loss of ND4 or ND4/ND5 still allows formation of substantial portion of CI (36). Also in humans, absence of ND4 or ND5 still allows formation of nuclear DNAencoded subcomplexes (34), possibly even displaying activity (27)(28)(29). ND3 mutation and absence of ND5 seem to have an effect on activity rather than assembly (28,37).…”

Deficiency of PHB complex impairs respiratory supercomplex formation and activates mitochondrial flashes

“…The PHB complex has been proposed to function as a mitochondrial membrane scaffold that might help to recruit membrane proteins to functional sites of the IMM (Osman et al, 2009b). Moreover, PHBs have been shown to be associated with complex IV subunits in yeast (Strub et al, 2011) and with complex I subunits in mammalian cells (Bourges et al, 2004), hinting at the possibility that PHBs might participate in the assembly of mitochondrial electron transport chain (ETC) complexes. Deficiency of PHBs leads to increased generation of reactive oxygen species (ROS) (Kathiria et al, 2012;Schleicher et al, 2008); however, the mechanism underlying PHBmediated regulation of mitochondrial ROS production is unknown.…”