ABSTRACT
Mitochondrial proteins require protein machineries called translocators in the outer and inner membranes for import into and sorting to their destination submitochondrial compartments. Among them, the TIM22 complex mediates insertion of polytopic membrane proteins into the inner membrane, and Tim22 constitutes its central insertion channel. Here we report that the conserved Cys residues of Tim22 form an intramolecular disulfide bond. By comparison of Tim22 Cys â Ser mutants with wild-type Tim22, we show that the disulfide bond of Tim22 stabilizes Tim22 especially at elevated temperature through interactions with Tim18, which are also important for the stability of the TIM22 complex. We also show that lack of the disulfide bond in Tim22 impairs the assembly of TIM22 pathway substrate proteins into the inner membrane especially when the TIM22 complex handles excess amounts of substrate proteins. Our findings provide a new insight into the mechanism of the maintenance of the structural and functional integrity of the TIM22 complex.
Subject(s)
Disulfides/metabolism , Mitochondrial Membrane Transport Proteins/metabolism , Mitochondrial Membranes/metabolism , Multiprotein Complexes/metabolism , Saccharomyces cerevisiae Proteins/metabolism , Saccharomyces cerevisiae/metabolism , Amino Acid Sequence , Antiporters/metabolism , Cysteine/genetics , Mitochondria/metabolism , Mitochondrial Membrane Transport Proteins/chemistry , Mitochondrial Precursor Protein Import Complex Proteins , Models, Biological , Molecular Sequence Data , Mutant Proteins/metabolism , Mutation/genetics , Protein Binding , Protein Stability , Protein Transport , Proteolysis , Saccharomyces cerevisiae/cytology , Saccharomyces cerevisiae/growth & development , Saccharomyces cerevisiae Proteins/chemistry , Serine/genetics , TemperatureABSTRACT
BACKGROUND: Epstein-Barr virus-associated hemophagocytic lymphohistiocytosis (EBV-HLH), also known as EBV-associated hemophagocytic syndrome, develops mostly in children and young adults and may be fatal. Early etoposide treatment has been confirmed to be effective in children. However, it is unclear whether the same treatment is useful in adults. PROCEDURE: To assess whether etoposide is effective in treating young adult cases, we retrospectively studied the therapeutic measures taken and outcomes in 20 young adult cases of EBV-HLH. Eleven cases were registered in our HLH study center in Kyoto and nine derived from the literature. The patients were between 17 and 33 years old and eight were males. The influence of gender, cell lineage (T- or natural killer-), EBV serology pattern, jaundice and treatment on the outcome was assessed. RESULTS AND CONCLUSIONS: Patients receiving etoposide within four weeks after diagnosis had a good prognosis as five of the seven patients survived compared to one of 13 not treated with etoposide or treated late (chi-square test for survival, P = 0.0095). The Kaplan-Meier analysis showed the 2.5-year survival of 85.7 +/- 13.2% in the early etoposide-treated patients, compared to 10.3 +/- 9.4% in the remaining patients (log-rank test, P = 0.0141). Thus, early etoposide treatment is effective in treating EBV-HLH in young adults as well as in children.
