Ignacio Arechaga

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A long-standing paradox in the study of T cell antigen recognition is that of the high specificity-low affinity T cell receptor (TCR)-major histocompatibility complex peptide (MHCp) interaction. The existence of multivalent TCRs could resolve this paradox because they can simultaneously improve the avidity observed for monovalent interactions and allow for(More)
The uncoupling protein (UCP) is uniquely expressed in brown adipose tissue, which is a thermogenic organ of mammals. The UCP uncouples mitochondrial respiration from ATP production by introducing a proton conducting pathway through the mitochondrial inner membrane. The activity of the UCP is regulated: nucleotide binding to the UCP inhibits proton(More)
In mitochondria, the hydrolytic activity of ATP synthase is regulated by a natural inhibitor protein, IF(1). The binding of IF(1) to ATP synthase depends on pH values, and below neutrality, IF(1) forms a stable complex with the enzyme. Bovine IF(1) has two oligomeric states, dimer and tetramer, depending on pH values. At pH 6.5, where it is active, IF(1)(More)
Since the chemiosmotic theory was proposed by Peter Mitchell in the 1960s, a major objective has been to elucidate the mechanism of coupling of the transmembrane proton motive force, created by respiration or photosynthesis, to the synthesis of ATP from ADP and inorganic phosphate. Recently, significant progress has been made towards establishing the(More)
Subunit c of the H(+) transporting ATP synthase is an essential part of its membrane domain that participates in transmembrane proton conduction. The annular architecture of the subunit c from different species has been previously reported. However, little is known about the type of interactions that affect the formation of c-rings in the ATPase complex.(More)
Type IV secretion systems (T4SS) mediate the transfer of DNA and protein substrates to target cells. TrwK, encoded by the conjugative plasmid R388, is a member of the VirB4 family, comprising the largest and most conserved proteins of T4SS. VirB4 was suggested to be an ATPase involved in energizing pilus assembly and substrate transport. However,(More)
Although memory T cells respond more vigorously to stimulation and they are more sensitive to low doses of antigen than naive T cells, the molecular basis of this increased sensitivity remains unclear. We have previously shown that the T cell receptor (TCR) exists as different-sized oligomers on the surface of resting T cells and that large oligomers are(More)
Recombinant membrane proteins in Escherichia coli are either expressed at relatively low level in the cytoplasmic membrane or they accumulate as inclusion bodies. Here, we report that the abundant over-production of subunit b of E. coli F(1)F(o) ATP synthase in the mutant host strains E. coli C41(DE3) and C43(DE3) is accompanied by the proliferation of(More)
In recent years, structural information on the F(1) sector of the ATP synthase has provided an insight into the molecular mechanism of ATP catalysis. The structure strongly supports the proposal that the ATP synthase works as a rotary molecular motor. Insights into the membrane domain have just started to emerge but more detailed structural information is(More)
Nature has endowed cells with powerful nanomotors to accomplish intricate mechanical tasks, such as the macromolecular transport across membranes occurring in cell division, bacterial conjugation, and in a wide variety of secretion systems. These biological motors couple the chemical energy provided by ATP hydrolysis to the mechanical work needed to(More)