Structure, mechanism and catalytic duality of thiamine-dependent enzymes

Thiamine is an essential cofactor that is required for processes of general metabolism amongst all organisms, and it is likely to have played a role in the earliest stages of the evolution of life. Here, we review from a structural perspective the enzymatic mechanisms that involve this cofactor. We explore asymmetry within homodimeric thiamine diphosphate (ThDP)-dependent enzyme structures and discuss how this may be correlated with the kinetic properties of half-of-the-sites reactivity, and negative cooperativity. It is likely these structural and kinetic hallmarks may arise through reciprocal coupling of active sites. This mode of communication between distant active sites is not unique to ThDP-dependent enzymes, but is widespread in other classes of oligomeric enzyme. Thus, it appears likely to be a general phenomenon reflecting a powerful mechanism of accelerating the rate of a chemical pathway. Finally, we speculate on the early evolutionary history of the cofactor and its ancient association with protein and RNA.     

Meta-analyses identify 13 loci associated with age at menopause and highlight DNA repair and immune pathways

To newly identify loci for age at natural menopause, we carried out a meta-analysis of 22 genome-wide association studies (GWAS) in 38,968 women of European descent, with replication in up to 14,435 women. In addition to four known loci, we identified 13 loci newly associated with age at natural menopause (at P < 5 × 10(-8)). Candidate genes located at these newly associated loci include genes implicated in DNA repair (EXO1, HELQ, UIMC1, FAM175A, FANCI, TLK1, POLG and PRIM1) and immune function (IL11, NLRP11 and PRRC2A (also known as BAT2)). Gene-set enrichment pathway analyses using the full GWAS data set identified exoDNase, NF-κB signaling and mitochondrial dysfunction as biological processes related to timing of menopause.     

Identification of ten loci associated with height highlights new biological pathways in human growth

Height is a classic polygenic trait, reflecting the combined influence of multiple as-yet-undiscovered genetic factors. We carried out a meta-analysis of genome-wide association study data of height from 15,821 individuals at 2.2 million SNPs, and followed up the strongest findings in >10,000 subjects. Ten newly identified and two previously reported loci were strongly associated with variation in height (P values from 4 x 10(-7) to 8 x 10(-22)). Together, these 12 loci account for approximately 2% of the population variation in height. Individuals with < or =8 height-increasing alleles and > or =16 height-increasing alleles differ in height by approximately 3.5 cm. The newly identified loci, along with several additional loci with strongly suggestive associations, encompass both strong biological candidates and unexpected genes, and highlight several pathways (let-7 targets, chromatin remodeling proteins and Hedgehog signaling) as important regulators of human stature. These results expand the picture of the biological regulation of human height and of the genetic architecture of this classical complex trait.     

Stabilization of microtubule dynamics at anaphase onset promotes chromosome segregation

Microtubules of the mitotic spindle form the structural basis for chromosome segregation. In metaphase, microtubules show high dynamic instability, which is thought to aid the 'search and capture' of chromosomes for bipolar alignment on the spindle. Microtubules suddenly become more stable at the onset of anaphase, but how this change in microtubule behaviour is regulated and how important it is for the ensuing chromosome segregation are unknown. Here we show that in the budding yeast Saccharomyces cerevisiae, activation of the phosphatase Cdc14 at anaphase onset is both necessary and sufficient for silencing microtubule dynamics. Cdc14 is activated by separase, the protease that triggers sister chromatid separation, linking the onset of anaphase to microtubule stabilization. If sister chromatids separate in the absence of Cdc14 activity, microtubules maintain high dynamic instability; this correlates with defects in both the movement of chromosomes to the spindle poles (anaphase A) and the elongation of the anaphase spindle (anaphase B). Cdc14 promotes localization of microtubule-stabilizing proteins to the anaphase spindle, and dephosphorylation of the kinetochore component Ask1 contributes to both the silencing of microtubule turnover and successful anaphase A.     

Apolipoprotein-mediated pathways of lipid antigen presentation

Peptide antigens are presented to T cells by major histocompatibility complex (MHC) molecules, with endogenous peptides presented by MHC class I and exogenous peptides presented by MHC class II. In contrast to the MHC system, CD1 molecules bind lipid antigens that are presented at the antigen-presenting cell (APC) surface to lipid antigen-reactive T cells. Because CD1 molecules survey endocytic compartments, it is self-evident that they encounter antigens from extracellular sources. However, the mechanisms of exogenous lipid antigen delivery to CD1-antigen-loading compartments are not known. Serum apolipoproteins are mediators of extracellular lipid transport for metabolic needs. Here we define the pathways mediating markedly efficient exogenous lipid antigen delivery by apolipoproteins to achieve T-cell activation. Apolipoprotein E binds lipid antigens and delivers them by receptor-mediated uptake into endosomal compartments containing CD1 in APCs. Apolipoprotein E mediates the presentation of serum-borne lipid antigens and can be secreted by APCs as a mechanism to survey the local environment to capture antigens or to transfer microbial lipids from infected cells to bystander APCs. Thus, the immune system has co-opted a component of lipid metabolism to develop immunological responses to lipid antigens.     

Diazoacetyl choline bromide

Zusammenfassung Es wird die Synthese von Diazoacetyl-cholin-bromid beschrieben. Die Verbindung zeigt in verschiedenen biologischen Präparaten starke acetyl-cholin-ähnliche Wirkung; sie wird von Acetylcholinesterase etwa 1.6×10⁴ mal langsamer als Acetylcholiniodid hydrolysiert. Die Photolyse gelingt mit Wellenlängen grösser als 315 nm. Das hauptsächliche Photolyseprodukt in Wasser ist Hydroxyacetyl-cholin-bromid. Es scheint — entsprechend dem stark elektronegativen Charakter der Trimethylammoniumgruppe — dieWolff'sche Umlagerung nur in untergeordnetem Masse einzutreten. Aufgrund dieser Befunde soll die Eignung der Verbindung zur Affinitätsmarkierung von Acetylcholinesterase, Cholinacetyltransferase und von Rezeptormolekeln untersucht werden.