The active transport of glycolytic pyruvate across the inner mitochondrial membrane is thought to involve two mitochondrial pyruvate carrier subunits, MPC1 and MPC2, assembled as a 150 kDa heterotypic oligomer. Here, the recombinant production of human MPC through a co-expression strategy is first described; however, substantial complex formation was not observed, and predominantly individual subunits were purified. In contrast to MPC1, which co-purifies with a host chaperone, we demonstrated that MPC2 homo-oligomers promote efficient pyruvate transport into proteoliposomes. The derived functional requirements and kinetic features of MPC2 resemble those previously demonstrated for MPC in the literature. Distinctly, chemical inhibition of transport is observed only for a thiazolidinedione derivative. The autonomous transport role for MPC2 is validated in cells when the ectopic expression of human MPC2 in yeast lacking endogenous MPC stimulated growth and increased oxygen consumption. Multiple oligomeric species of MPC2 across mitochondrial isolates, purified protein and artificial lipid bilayers suggest functional high-order complexes. Significant changes in the secondary structure content of MPC2, as probed by synchrotron radiation circular dichroism, further supports the interaction between the protein and ligands. Our results provide the initial framework for the independent role of MPC2 in homeostasis and diseases related to dysregulated pyruvate metabolism.

During the process of endochondral bone formation, chondrocytes and osteoblasts mineralize their extracellular matrix (ECM) by promoting the synthesis of hydroxyapatite (HA) seed crystals in the sheltered interior of membranelimited matrix vesicles (MVs). Several lipid and proteins present in the membrane of the MVs mediate the interactions of MVs with the ECM and regulate the initial mineral deposition and posterior propagation. Among the proteins of MV membranes, ion transporters control the availability of phosphate and calcium needed for initial HA deposition. Phosphatases (orphan phosphatase 1, ectonucleotide pyrophosphatase/ phosphodiesterase 1 and tissue-nonspecific alkaline phosphatase) play a crucial role in controlling the inorganic pyrophosphate/inorganic phosphate ratio that allows MVmediated initiation of mineralization. The lipidic microenvironment can help in the nucleation process of first crystals and also plays a crucial physiological role in the function of MVassociated enzymes and transporters (type III sodiumdependent phosphate transporters, annexins and Na + /K + ATPase). The whole process is mediated and regulated by the action of several molecules and steps, which make the process complex and highly regulated. Liposomes and proteoliposomes, as models of biological membranes, facilitate the understanding of lipid-protein interactions with emphasis on the properties of physicochemical and biochemical processes. In this review, we discuss the use of proteoliposomes as multiple protein carrier systems intended to mimic the various functions of MVs during the initiation and propagation of mineral growth in the course of biomineralization. We focus on studies applying biophysical tools to characterize the biomimetic models in order to gain an understanding of the importance of lipid-protein and lipid-lipid interfaces throughout the process.Keywords Lipid microenvironment . Biomineralization . Matrix vesicles . Liposome . Proteoliposome . Hydroxyapatite Mineralization process and the biogenesis of matrix vesiclesMineralization of cartilage and bone occurs by a series of physicochemical and biochemical processes that together facilitate the deposition of calcium phosphate. The deposited calcium phosphate is subsequently converted into hydroxyapatite (HA) [Ca 10 (PO 4 ) 6 (OH) 2 ] in specific areas of the extracellular matrix (ECM). Various experiments have revealed the presence of HA crystals both inside and outside collagen fibrils in the ECM (McNally et al. 2012) and also within the

In this study, we obtained unprecedented AFM images of the Na,K-ATPase (NKA) pump after being reconstituted into DPPC and DPPC:DPPE liposomes.