Characterization of low abundant membrane proteins using the protein sequence tag technology

About 25% of open reading frames in fully sequenced genomes are estimated to encode transmembrane proteins that represent valuable targets for drugs. However, the global analysis of membrane proteins has been proven to be problematic, e.g., because of their very amphiphilic nature. In this paper, we show that the recently published Protein Sequence Tag (PST) technology combined with an efficient sample preparation is a powerful method to perform protein analysis of highly enriched membrane fractions. The PST approach is a gel-free proteomics tool for the analysis of proteins, which relies on a "sampling" strategy by isolating N-terminal protein sequence tags from cyanogen bromide cleaved proteins. The identification of these N-terminal PST peptides is based on LC-MS/MS. The effectiveness of the technology is demonstrated for a membrane fraction, which was isolated from crude mitochondria of yeast after alkaline sodium carbonate treatment. The PST approach performed on this fraction analyzed 148 proteins, whereas 84% are identified as membrane proteins. More interestingly, among these membrane proteins 56% are predicted to be of low abundance. These encouraging results are an important step toward the development of a quantitative PST approach (qPST) for the differential display of membrane protein analysis.     

Mismatch repair and DNA damage signalling

Postreplicative mismatch repair (MMR) increases the fidelity of DNA replication by up to three orders of magnitude, through correcting DNA polymerase errors that escaped proofreading. MMR also controls homologous recombination (HR) by aborting strand exchange between divergent DNA sequences. In recent years, MMR has also been implicated in the response of mammalian cells to DNA damaging agents. Thus, MMR-deficient cells were shown to be around 100-fold more resistant to killing by methylating agents of the S(N)1type than cells with functional MMR. In the case of cisplatin, the sensitivity difference was lower, typically two- to three-fold, but was observed in all matched MMR-proficient and -deficient cell pairs. More controversial is the role of MMR in cellular response to other DNA damaging agents, such as ionizing radiation (IR), topoisomerase poisons, antimetabolites, UV radiation and DNA intercalators. The MMR-dependent DNA damage signalling pathways activated by the above agents are also ill-defined. To date, signalling cascades involving the Ataxia telangiectasia mutated (ATM), ATM- and Rad3-related (ATR), as well as the stress-activated kinases JNK/SAPK and p38alpha have been linked with methylating agent and 6-thioguanine (TG) treatments, while cisplatin damage was reported to activate the c-Abl and JNK/SAPK kinases in MMR-dependent manner. MMR defects are found in several different cancer types, both familiar and sporadic, and it is possible that the involvement of the MMR system in DNA damage signalling play an important role in transformation. The scope of this article is to provide a brief overview of the recent literature on this subject and to raise questions that could be addressed in future studies.     

Micro-thermal focusing field-flow fractionation

Focusing mechanism was effectively exploited to separate large (micrometer-size) particles by using new micro-thermal field-flow fractionation (micro-TFFF). It has been shown that the retention order of micrometer-size particles at high field strength can be explained by the mechanism of steric exclusion only at lowest flow rates of the carrier liquid. A simplistic, purely mechanical model of steric exclusion is not accurate to describe the retention at higher flow rates where the focusing phenomenon appears. Despite the fact that the thickness of the channel for micro-FFF cannot be reduced without taking into account a possible deterioration of the separation due to the contribution of "steric exclusion" mechanism, this paper demonstrates, in agreement with our previous results, that if the operational conditions were conveniently chosen, namely a low flow rate, a reasonable fit of the experimental retention data with the theory of steric exclusion mechanism in FFF was found and the separation of micron-size particles can be accomplished. However, high selectivity and resolution and high-speed separation were achieved if the focusing effect has clearly dominated the FFF mechanism. As a result, it seems that the micro-TFFF is the most universal technique which can be applied for the separation of the synthetic and natural macromolecules within an extended range of molar masses up to ultra-high molar masses and for the particles of various chemical nature and origin in a nano-size range as well as for large (micrometers) particles. Until nowadays, only sedimentation and flow field-flow fractionation techniques in so called "steric" modes were applied for the separations of large size particles. This application of micro-TFFF in focusing mode for the separation of large size particles is the first one described in the literature.     

Utilization of newly developed immobilized enzyme reactors for preparation and study of immunoglobulin G fragments

The newly developed immobilized enzyme reactors (IMERs) with proteolytic enzymes chymotrypsin, trypsin or papain were used for specific fragmentation of high molecular-mass and heterogeneous glycoproteins immunoglobulin G (IgG) and crystallizable fragment of IgG (Fc). The efficiency of splitting or digestion were controlled by RP-HPLC. The specificity of digestion by trypsin reactor was controlled by MS. IMERs (trypsin immobilized on magnetic microparticles focused in a channel of magnetically active microfluidic device) was used for digestion of the whole IgG molecule. The sufficient conditions for IgG digestion in microfluidic device (flow rate, ratio S:E, pH, temperature) were optimized. It was confirmed that the combination of IMERs with microfluidic device enables efficient digestion of highly heterogeneous glycoproteins such as IgG in extremely short time and minimal reaction volume.     

Efficacy of repeated intrathecal triamcinolone acetonide application in progressive multiple sclerosis patients with spinal symptoms

Background

There are controversial results on the efficacy of the abandoned, intrathecal predominant methylprednisolone application in multiple sclerosis (MS) in contrast to the proven effectiveness in intractable postherpetic neuralgia.

Methods

We performed an analysis of the efficacy of the application of 40 mg of the sustained release steroid triamcinolone acetonide (TCA). We intrathecally injected in sterile saline dissolved TCA six times within three weeks on a regular basis every third day in 161 hospitalized primary and predominant secondary progressive MS patients with spinal symptoms. The MS patients did not experience an acute onset of exacerbation or recent distinct increased progression of symptoms. We simultaneously scored the MS patients with the EDSS and the Barthel index, estimated the walking distance and measured somatosensory evoked potentials. Additionally the MS patients received a standardized rehabilitation treatment.

Results

EDSS score and Barthel index improved, walking distance increased, latencies of somatosensory evoked potentials of the median and tibial nerves shortened in all MS patients with serial evaluation (p < 0.0001 for all variables). Side effects were rare, five patients stopped TCA application due to onset of a post lumbar puncture syndrome.

Conclusions

Repeated intrathecal TCA application improves spinal symptoms, walking distance and SSEP latencies in progressive MS patients in this uncontrolled study. Future trials should evaluate the long-term benefit of this invasive treatment.

     

Replicator dynamics for optional public good games

The public goods game represents a straightforward generalization of the prisoner's dilemma to an arbitrary number of players. Since the dominant strategy is to defect, both classical and evolutionary game theory predict the asocial outcome that no player contributes to the public goods. In contrast to the compulsory public goods game, optional participation provides a natural way to avoid deadlocks in the state of mutual defection. The three resulting strategies--collaboration or defection in the public goods game, as well as not joining at all--are studied by means of a replicator dynamics, which can be completely analysed in spite of the fact that the payoff terms are nonlinear. If cooperation is valuable enough, the dynamics exhibits a rock-scissors-paper type of cycling between the three strategies, leading to sizeable average levels of cooperation in the population. Thus, voluntary participation makes cooperation feasible. But for each strategy, the average payoff value remains equal to the earnings of those not participating in the public goods game.     

Solution structure and dynamics of Crh, the Bacillus subtilis catabolite repression HPr

The solution structure and dynamics of the Bacillus subtilis HPr-like protein, Crh, have been investigated using NMR spectroscopy. Crh exhibits high sequence identity (45 %) to the histidine-containing protein (HPr), a phospho-carrier protein of the phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system, but contains no catalytic His15, the site of PEP-dependent phosphorylation in HPr. Crh also forms a mixture of monomers and dimers in solution whereas HPr is known to be monomeric. Complete backbone and side-chain assignments were obtained for the monomeric form, and 60 % of the dimer backbone resonances; allowing the identification of the Crh dimer interface from chemical-shift mapping. The conformation of Crh was determined to a precision of 0.46(+/-0.06) A for the backbone atoms, and 1.01(+/-0.08) A for the heavy atoms. The monomer structure is similar to that of known HPr 2.67(+/-0.22) A (C(alpha) rmsd), but has a few notable differences, including a change in the orientation of one of the helices (B), and a two-residue shift in beta-sheet pairing of the N-terminal strand with the beta4 strand. This shift results in a shortening of the surface loop present in HPr and consequently provides a flatter surface in the region of dimerisation contact, which may be related to the different oligomeric nature of these two proteins. A binding site of phospho-serine(P-Ser)-Crh with catabolite control protein A (CcpA) is proposed on the basis of highly conserved surface side-chains between Crh and HPr. This binding site is consistent with the model of a dimer-dimer interaction between P-Ser-Crh and CcpA. (15)N relaxation measured in the monomeric form also identified differential local mobility in the helix B which is located in the vicinity of this site.     

Subunit specificity and interaction domain between GABA(A) receptor-associated protein (GABARAP) and GABA(A) receptors

GABARAP (GABA(A) receptor-associated protein) interacts with both microtubules and GABA(A) receptors in vitro and in vivo and is capable of modulating receptor channel kinetics. In this study, we use the intracellular loop of 15 GABA(A) receptor subunits to show that the interaction between GABARAP and GABA(A) receptor is specific for the gamma subunits. Pharmacological characterization of proteins purified by GABARAP affinity column indicates that native GABA(A) receptors interact with GABARAP. Quantitative yeast two-hybrid assays were used to identify the interaction domain in the gamma2 subunit for GABARAP binding, and to identify the interaction domain in GABARAP for GABA(A) receptor binding. A peptide corresponding to the GABARAP interaction domain in the gamma2 subunit was used to inhibit the interaction between GABARAP and the gamma2 subunit. In addition, the ability of GABARAP to promote cluster formation of recombinant receptors expressed in QT-6 fibroblasts was inhibited by a membrane-permeable form of this peptide in a time-dependent manner. The establishment of a model for GABARAP-induced clustering of GABA(A) receptors in living cells and the identification of subunit specificity and interaction domains in the interaction between GABARAP and GABA(A) receptors is a step in dissecting the function of GABARAP in GABA(A) receptor clustering and/or targeting.