Mitochondria is the power stations of the cell. There are many different embedded proteins http://www.cusabio.com/catalog-13-1.html in the membranes of mitochondria. These proteins perform vital functions for the mitochondria. A research team from the University of Freiburg found that lipids help a protein machinery to integrate proteins into the outer membrane of mitochondria. It is well known that lipids are fatlike substances forming the basic building blocks of biological membranes.
Mitochondria perform key functions for the cell, like producing the energy for cell metabolism. Mitochondrial dysfunctions can cause severe neurological diseases. Certain proteins of the outer membrane form a beta-barrel structure. There proteins are essential for the development of the mitochondria. They enable the transport of proteins and metabolic intermediates, or metabolites. Ribosomes within the cytosol -- the cell fluid -- produce the beta-barrel proteins. The protein translocases, which are two protein machineries in the outer membrane of the mitochondria, integrate the barrel structures into the membrane. The translocase of the outer membrane is called TOM complex and it transports the proteins from the cytosol into the mitochondria. Then the SAM complex integrates the proteins into the membrane. Scientists have well studied TOM and SAM. But the role of lipids is still not clear.
In mitochondria, the main components of the membranes are the phospholipids, of which phosphatidylcholine (PC) is the most abundant one. The research team discovered a previously unknown role of PC in the development of beta-barrel proteins. It was discovered that the function of the SAM complex depends on the concentration of PC in the membrane. Scientists analysed the mitochondria of baker's yeast mutants, which had a significantly lower concentration of PC. The results demonstrated that the integration of the beta-barrel proteins into the outer membrane is impaired in the mutated baker's yeast. This can be explained by the fact that the function and stability of the SAM complex in these mutants is disturbed. In contrast, the activity of the TOM complex is not inhibited. This means that beta-barrel proteins can pass the TOM complex unimpeded, while their integration into the outer membrane does not occur at full speed when the concentration of PC is reduced.
This study indicates that protein machinery and lipids are closely connected in protein transport and that the integration of the beta-barrel proteins http://www.cusabio.com/ in the target membrane depends on the composition of the membrane.
