Selective transport of pyruvate across the inner mitochondrial membrane by the mitochondrial pyruvate carrier (MPC) is a fundamental step that couples cytosolic and mitochondrial metabolism. The recent molecular identification of the MPC complex has revealed two interacting subunits, MPC1 and MPC2. Although in yeast, an additional subunit, MPC3, can functionally replace MPC2, no alternative MPC subunits have been described in higher eukaryotes. Here, we report for the first time the existence of a novel MPC subunit termed MPC1-like (MPC1L), which is present uniquely in placental mammals. MPC1L shares high sequence, structural, and topological homology with MPC1. In addition, we provide several lines of evidence to show that MPC1L is functionally equivalent to MPC1: 1) when co-expressed with MPC2, it rescues pyruvate import in a MPC-deleted yeast strain; 2) in mammalian cells, it can associate with MPC2 to form a functional carrier as assessed by bioluminescence resonance energy transfer; 3) in MPC1 depleted mouse embryonic fibroblasts, MPC1L rescues the loss of pyruvate-driven respiration and stabilizes MPC2 expression; and 4) MPC1-and MPC1L-mediated pyruvate imports show similar efficiency. However, we show that MPC1L has a highly specific expression pattern and is localized almost exclusively in testis and more specifically in postmeiotic spermatids and sperm cells. This is in marked contrast to MPC1/MPC2, which are ubiquitously expressed throughout the organism. To date, the biological importance of this alternative MPC complex during spermatogenesis in placental mammals remains unknown. Nevertheless, these findings open up new avenues for investigating the structure-function relationship within the MPC complex.The metabolic balance between glycolysis and oxidative phosphorylation (OXPHOS) 2 is of crucial importance in determining cell function and fate. Rapidly proliferating cells rely preferentially on glycolysis despite its lower yield of ATP, because glycolytic intermediates efficiently meet the anabolic needs for sustained cell growth. In rapidly dividing cells, this occurs even in the presence of oxygen, a process called aerobic glycolysis, or the Warburg effect (1, 2). Differentiated cells rely more heavily on OXPHOS to meet the energy demands associated with their specialization. In addition, a shift from glycolytic to oxidative metabolism is necessary for the differentiation process to occur (2-4), and conversely, a hallmark of cancer lies in the rewiring of cellular metabolism toward increased glycolytic flux (5). Pyruvate, the end product of glycolysis, is imported into the mitochondrial matrix where it fuels the TCA cycle and thereby provides electrons and reducing equivalents to the respiratory chain. Pyruvate-derived acetyl-CoA can also be used as an anabolic substrate for the synthesis of lipids and amino acids. Thus, elucidating the molecular mechanisms that determine the intracellular fate of pyruvate is important for understanding the control of cell metabolism and ultimately of cell funct...
