Mass spectrometry is a vital tool for molecular characterization, and the allied technique of ion mobility is enhancing many areas of (bio)chemical analysis. Strong synergy arises between these two techniques because of their ability to ascertain complementary information about gas-phase ions. Ion mobility separates ions (from small molecules up to megadalton protein complexes) based on their differential mobility through a buffer gas. Ion mobility-mass spectrometry (IM-MS) can thus act as a tool to separate complex mixtures, to resolve ions that may be indistinguishable by mass spectrometry alone, or to determine structural information (for example rotationally averaged cross-sectional area), complementary to more traditional structural approaches. Finally, IM-MS can be used to gain insights into the conformational dynamics of a system, offering a unique means of characterizing flexibility and folding mechanisms. This Review critically describes how IM-MS has been used to enhance various areas of chemical and biophysical analysis.

b; Université catholique de Louvain, Brussels, Belgium c Eukaryotic elongation factor 2 kinase (eEF2K), an atypical calmodulin-dependent protein kinase, phosphorylates and inhibits eEF2, slowing down translation elongation. eEF2K contains an N-terminal catalytic domain, a C-terminal ␣-helical region and a linker containing several regulatory phosphorylation sites. eEF2K is expressed at high levels in certain cancers, where it may act to help cell survival, e.g., during nutrient starvation. However, it is a negative regulator of protein synthesis and thus cell growth, suggesting that cancer cells may possess mechanisms to inhibit eEF2K under good growth conditions, to allow protein synthesis to proceed. We show here that the mTORC1 pathway and the oncogenic Ras/Raf/MEK/extracellular signal-regulated kinase (ERK) pathway cooperate to restrict eEF2K activity. We identify multiple sites in eEF2K whose phosphorylation is regulated by mTORC1 and/or ERK, including new ones in the linker region. We demonstrate that certain sites are phosphorylated directly by mTOR or ERK. Our data reveal that glycogen synthase kinase 3 signaling also regulates eEF2 phosphorylation. In addition, we show that phosphorylation sites remote from the N-terminal calmodulin-binding motif regulate the phosphorylation of N-terminal sites that control CaM binding. Mutations in the former sites, which occur in cancer cells, cause the activation of eEF2K. eEF2K is thus regulated by a network of oncogenic signaling pathways.

The mechanisms of oxidative N-dealkylation of amines by heme enzymes including peroxidases and cytochromes P450 and by functional models for the active Compound I species have long been studied. A debated issue has concerned in particular the character of the primary step initiating the oxidation sequence, either a hydrogen atom transfer (HAT) or an electron transfer (ET) event, facing problems such as the possible contribution of multiple oxidants and complex environmental effects. In the present study, an oxo iron(IV) porphyrin radical cation intermediate 1, [(TPFPP)*+ Fe(IV)=O]+ (TPFPP = meso-tetrakis (pentafluorophenyl)porphinato dianion), functional model of Compound I, has been produced as a bare species. The gas-phase reaction with amines (A) studied by ESI-FT-ICR mass spectrometry has revealed for the first time the elementary steps and the ionic intermediates involved in the oxidative activation. Ionic products are formed involving ET (A*+, the amine radical cation), formal hydride transfer (HT) from the amine ([A(-H)]+, an iminium ion), and oxygen atom transfer (OAT) to the amine (A(O), likely a carbinolamine product), whereas an ionic product involving a net initial HAT event is never observed. The reaction appears to be initiated by an ET event for the majority of the tested amines which included tertiary aliphatic and aromatic amines as well as a cyclic and a secondary amine. For a series of N,N-dimethylanilines the reaction efficiency for the ET activated pathways was found to correlate with the ionization energy of the amine. A stepwise pathway accounts for the C-H bond activation resulting in the formal HT product, namely a primary ET process forming A*+, which is deprotonated at the alpha-C-H bond forming an N-methyl-N-arylaminomethyl radical, A(-H)*, readily oxidized to the iminium ion, [A(-H)]+. The kinetic isotope effect (KIE) for proton transfer (PT) increases as the acidity of the amine radical cation increases and the PT reaction to the base, the ferryl group of (TPFPP)Fe(IV)=O, approaches thermoneutrality. The ET reaction displayed by 1 with gaseous N,N-dimethylaniline finds a counterpart in the ET reactivity of FeO+, reportedly a potent oxidant in the gas phase, and with the barrierless ET process for a model (P)*+ Fe(IV)=O species (where P is the porphine dianion) as found by theoretical calculations. Finally, the remarkable OAT reactivity of 1 with C6F5N(CH3)2 may hint to a mechanism along a route of diverse spin multiplicity.

No abstract

Number of tables: 2 Number of references: 54Number of words in the abstract: 246 Number of words in the introduction: 722Number of words in the discussion: 1450 Abbreviations ADME, absorption, distribution, metabolism and excretion; BSA, bovine serum albumin; DDI, drugdrug interaction; DME, drug-metabolizing enzyme; GO, Gene Ontology project; HLM, human liver microsomes; HPLC, high performance liquid chromatography; IMS, ion-mobility spectrometry; IVIVE, in vitro-in vivo extrapolation; LC-MS, liquid chromatography in conjunction with mass spectrometry; LysC, lysyl endopeptidase; MS/MS, tandem mass spectrometry; MALDI-TOF, matrix- We suggest that protein concentrations used in pharmacokinetic predictions and scaling to in vivo clinical situations (PBPK-IVIVE) should be referenced instead to tissue mass. DMD # 747324

Protein post-translational modifications (PTMs) are critically important in regulating both protein structure and function, often in a rapid and reversible manner. Due to its sensitivity and vast applicability, mass spectrometry (MS) has become the technique of choice for analyzing PTMs. Whilst the "bottom-up' analytical approach, in which proteins are proteolyzed generating peptides for analysis by MS, is routinely applied and offers some advantages in terms of ease of analysis and lower limit of detection, "top-down" MS, describing the analysis of intact proteins, yields unique and highly valuable information on the connectivity and therefore combinatorial effect of multiple PTMs in the same polypeptide chain. In this review, the state of the art in top-down MS will be discussed, covering the main instrumental platforms and ion activation techniques. Moreover, the way that this approach can be used to gain insights on the combinatorial effect of multiple post-translational modifications and how this information can assist in studying physiologically relevant systems at the molecular level will also be addressed.

No abstract

Prototypical Meisenheimer complexes are characterized as stable, covalent intermediates in the gas phase, using a novel, highly diagnostic spectroscopic technique that exploits the potential emerging from the combination of mass spectrometry with an IR FEL radiation source