Carrier mediated GABA translocation into rat brain mitochondria

GABA added to rat brain mitochondria causes oxidation of intramitochondrial NAD(P)H as well as inducing glutamate efflux from the mitochondrial matrix. The rate of NAD(P)H oxidation shows saturation characteristics, depends on GABA transport across the mitochondrial membrane and is inhibited by non-penetrant compounds and by the metal-complexing agent bathophenanthroline. These results show the existence of a specific GABA carrier. Inhibition studies strongly suggest the existence of two separate binding sites, namely the GABA binding site and the dicarboxylates binding site, as well as suggest the presence of a metal ion (ions) at GABA binding site. The occurrence of a GABA/GLUTAMATE antiport is proposed which allows a cyclical route to account for GABA synthesis and degradation in brain.     

RBM10 regulates alternative splicing

RBM10, originally called S1-1, is a nuclear RNA-binding protein with domains characteristic of RNA processing proteins. It has been reported that RBM10 constitutes spliceosome complexes and that RBM5, a close homologue of RBM10, regulates alternative splicing of apoptosis-related genes, Fas and cFLIP. In this study, we examined whether RBM10 has a regulatory function in splicing similar to RBM5, and determined that it indeed regulates alternative splicing of Fas and Bcl-x genes. RBM10 promotes exon skipping of Fas pre-mRNA as well as selection of an internal 5′-splice site in Bcl-x pre-mRNA. We propose a consensus RBM10-binding sequence at 5′-splice sites of target exons and a mechanistic model of RBM10 action in the alternative splicing.     

The RNA recognition motif domains of RBM5 are required for RNA binding and cancer cell proliferation inhibition

RBM5 is a known putative tumor suppressor gene that has been shown to function in cell growth inhibition by modulating apoptosis. RBM5 also plays a critical role in alternative splicing as an RNA binding protein. However, it is still unclear which domains of RBM5 are required for RNA binding and related functional activities. We hypothesized the two putative RNA recognition motif (RRM) domains of RBM5 spanning from amino acids 98–178 and 231–315 are essential for RBM5-mediated cell growth inhibition, apoptosis regulation, and RNA binding. To investigate this hypothesis, we evaluated the activities of the wide-type and mutant RBM5 gene transfer in low-RBM5 expressing A549 cells. We found that, unlike wild-type RBM5 (RBM5-wt), a RBM5 mutant lacking the two RRM domains (RBM5-ΔRRM), is unable to bind RNA, has compromised caspase-2 alternative splicing activity, lacks cell proliferation inhibition and apoptosis induction function in A549 cells. These data provide direct evidence that the two RRM domains of RBM5 are required for RNA binding and the RNA binding activity of RBM5 contributes to its function on apoptosis induction and cell growth inhibition.     

Determination of the physiological dimer interface of the PhoQ sensor domain

PhoQ is the transmembrane sensor kinase of the phoPQ two-component system, which detects and responds to divalent cations and antimicrobial peptides and can trigger bacterial virulence. Despite their ubiquity and importance in bacterial signaling, the structure and molecular mechanism of the sensor kinases is not fully understood. Frequently, signals are transmitted from a periplasmic domain in these proteins to the cytoplasmic kinase domains via an extended dimeric interface, and the PhoQ protein would appear to follow this paradigm. However, the isolated truncated periplasmic domain of PhoQ dimerizes poorly, so it has been difficult to distinguish the relevant interface in crystal structures of the PhoQ periplasmic domain. Thus, to determine the arrangement of the periplasmic domains of Escherichia coli PhoQ in the physiological homodimer, disulfide-scanning mutagenesis was used. Single cysteine substitutions were introduced along the N-terminal helix of the periplasmic region, and the degree of cross-linking in each protein variant was determined by Western blotting and immunodetection. The results were subjected to periodicity analysis to generate a profile that provides information concerning the C^β distances between corresponding residues at the interface. This profile, together with a rigid-body search procedure, side-chain placement, and energy minimization, was used to build a model of the dimer arrangement. The final model proved to be highly compatible with one of the PhoQ crystal structures, 3BQ8, indicating that 3BQ8 is representative of the physiological arrangement. The model of the periplasmic region is also compatible with a full-length PhoQ protein in which a four-helix bundle forms in the membrane. The membrane four-helix bundle has been proposed for other sensor kinases and is thought to have a role in the mechanism of signal transduction; our model supports the idea that signaling through a membrane four-helix bundle is a widespread mechanism in the transmembrane sensor kinases.     

Pharmacologic modulation of RNA splicing enhances anti-tumor immunity

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RBM10: Harmful or helpful‐many factors to consider

RBM10 is an RNA binding motif (RBM) protein expressed in most, if not all, human and animal cells. Interest in RBM10 is rapidly increasing and its clinical importance is highlighted by its identification as the causative agent of TARP syndrome, a developmental condition that significantly impacts affected children. RBM10's cellular functions are beginning to be explored, with initial studies demonstrating a tumor suppressor role. Very recently, however, contradictory results have emerged, suggesting a tumor promoter role for RBM10. In this review, we describe the current state of knowledge on RBM10, and address this dichotomy in RBM10 function. Furthermore, we discuss what may be regulating RBM10 function, particularly the importance of RBM10 alternative splicing, and the relationship between RBM10 and its paralogue, RBM5. As RBM10‐related work is gaining momentum, it is critical that the various aspects of RBM10 molecular biology revealed by recent studies be considered moving forward. It is only if these recent advances in RBM10 structure and function are considered that a clearer insight into RBM10 function, and the disease states with which RBM10 mutation is associated, will be gained.