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Assembly Pathway (assembly + pathway)
Selected AbstractsEvolution of peptidoglycan biosynthesis under the selective pressure of antibiotics in Gram-positive bacteriaFEMS MICROBIOLOGY REVIEWS, Issue 2 2008Jean-Luc Mainardi Abstract Acquisition of resistance to the two classes of antibiotics therapeutically used against Gram-positive bacteria, the glycopeptides and the ,-lactams, has revealed an unexpected flexibility in the peptidoglycan assembly pathway. Glycopeptides select for diversification of the fifth position of stem pentapeptides because replacement of d -Ala by d -lactate or d -Ser at this position prevents binding of the drugs to peptidoglycan precursors. The substitution is generally well tolerated by the classical d,d -transpeptidases belonging to the penicillin-binding protein family, except by low-affinity enzymes. Total elimination of the fifth residue by a d,d -carboxypeptidase requires a novel cross-linking enzyme able to process the resulting tetrapeptide stems. This enzyme, an l,d -transpeptidase, confers cross-resistance to ,-lactams and glycopeptides. Diversification of the side chain of the precursors, presumably in response to the selective pressure of peptidoglycan endopeptidases, is controlled by aminoacyl transferases of the Fem family that redirect specific aminoacyl-tRNAs from translation to peptidoglycan synthesis. Diversification of the side chains has been accompanied by a parallel divergent evolution of the substrate specificity of the l,d -transpeptidases, in contrast to the d,d -transpeptidases, which display an unexpected broad specificity. This review focuses on the role of antibiotics in selecting or counter-selecting diversification of the structure of peptidoglycan precursors and their mode of polymerization. [source] Pathogen evasion strategies for the major histocompatibility complex class I assembly pathwayIMMUNOLOGY, Issue 1 2008Antony N. Antoniou Summary Major histocompatibility complex (MHC) class I molecules bind and present short antigenic peptides from endogenously or exogenously derived sources to CD8+ cytotoxic T lymphocytes (CTL), with recognition of a foreign peptide normally targeting the cell for lysis. It is generally thought that the high level of MHC polymorphism, which is concentrated mostly within the peptide-binding groove, is driven by the ,evolutionary arms race' against pathogens. Many pathogens have developed novel and intriguing mechanisms for evading the continuous sampling of the intracellular and intercellular environments by MHC molecules, none more so than viruses. The characterization of immunoevasion mechanisms has improved our understanding of MHC biology. This review will highlight our current understanding of the MHC class I biosynthetic pathway and how it has been exploited by pathogens, especially viruses, to potentially evade CTL recognition. [source] Biosynthesis of the red antibiotic, prodigiosin, in Serratia: identification of a novel 2-methyl-3-n-amyl-pyrrole (MAP) assembly pathway, definition of the terminal condensing enzyme, and implications for undecylprodigiosin biosynthesis in StreptomycesMOLECULAR MICROBIOLOGY, Issue 4 2005Neil R. Williamson Summary The biosynthetic pathway of the red-pigmented antibiotic, prodigiosin, produced by Serratia sp. is known to involve separate pathways for the production of the monopyrrole, 2-methyl-3-n-amyl-pyrrole (MAP) and the bipyrrole, 4-methoxy-2,2,-bipyrrole-5-carbaldehyde (MBC) which are then coupled in the final condensation step. We have previously reported the cloning, sequencing and heterologous expression of the pig cluster responsible for prodigiosin biosynthesis in two Serratia sp. In this article we report the creation of in-frame deletions or insertions in every biosynthetic gene in the cluster from Serratia sp. ATCC 39006. The biosynthetic intermediates accumulating in each mutant have been analysed by LC-MS, cross-feeding and genetic complementation studies. Based on these results we assign specific roles in the biosynthesis of MBC to the following Pig proteins: PigI, PigG, PigA, PigJ, PigH, PigM, PigF and PigN. We report a novel pathway for the biosynthesis of MAP, involving PigD, PigE and PigB. We also report a new chemical synthesis of MAP and one of its precursors, 3-acetyloctanal. Finally, we identify the condensing enzyme as PigC. We reassess the existing literature and discuss the significance of the results for the biosynthesis of undecylprodigiosin by the Red cluster in Streptomyces coelicolor A3(2). [source] Pressure dissociation studies provide insight into oligomerization competence of temperature-sensitive folding mutants of P22 tailspikePROTEIN SCIENCE, Issue 6 2004Brian G. Lefebvre Abstract Several temperature-sensitive folding (tsf) mutants of the tailspike protein from bacteriophage P22 have been found to fold with lower efficiency than the wild-type sequence, even at lowered temperatures. Previous refolding studies initiated from the unfolded monomer have indicated that the tsf mutations decrease the rate of structured monomer formation. We demonstrate that pressure treatment of the tailspike aggregates provides a useful tool to explore the effects of tsf mutants on the assembly pathway of the P22 tailspike trimer. The effects of pressure on two different tsf mutants, G244R and E196K, were explored. Pressure treatment of both G244R and E196K aggregates produced a folded trimer. E196K forms almost no native trimer in in vitro refolding experiments, yet it forms a trimer following pressure in a manner similar to the native tailspike protein. In contrast, trimer formation from pressure-treated G244R aggregates was not rapid, despite the presence of a G244R dimer after pressure treatment. The center-of-mass shifts of the fluorescence spectra under pressure are nearly identical for both tsf aggregates, indicating that pressure generates similar intermediates. Taken together, these results suggest that E196K has a primary defect in formation of the ,-helix during monomer collapse, while G244R is primarily an assembly defect. [source] Generation of branched actin networks: assembly and regulation of the N-WASP and WAVE molecular machinesBIOESSAYS, Issue 2 2010Emmanuel Derivery Abstract The Arp2/3 complex is a molecular machine that generates branched actin networks responsible for membrane remodeling during cell migration, endocytosis, and other morphogenetic events. This machine requires activators, which themselves are multiprotein complexes. This review focuses on recent advances concerning the assembly of stable complexes containing the most-studied activators, N-WASP and WAVE proteins, and the level of regulation that is provided by these complexes. N-WASP is the paradigmatic auto-inhibited protein, which is activated by a conformational opening. Even though this regulation has been successfully reconstituted in vitro with isolated N-WASP, the native dimeric complex with a WIP family protein has unique additional properties. WAVE proteins are part of a pentameric complex, whose basal state and activated state when bound to the Rac GTPase were recently clarified. Moreover, this review attempts to put together diverse observations concerning the WAVE complex in the conceptual frame of an in vivo assembly pathway that has gained support from the recent identification of a precursor. [source] Centrioles to basal bodies in the spermiogenesis of Mastotermes darwiniensis (Insecta, Isoptera)CYTOSKELETON, Issue 5 2009Maria Giovanna Riparbelli Abstract In addition to their role in centrosome organization, the centrioles have another distinct function as basal bodies for the formation of cilia and flagella. Centriole duplication has been reported to require two alternate assembly pathways: template or de novo. Since spermiogenesis in the termite Mastotermes darwiniensis lead to the formation of multiflagellate sperm, this process represents a useful model system in which to follow basal body formation and flagella assembly. We present evidence of a possible de novo pathway for basal body formation in the differentiating germ cell. This cell also contains typical centrosomal proteins, such as centrosomin, pericentrin-like protein, ,-tubulin, that undergo redistribution as spermatid differentiation proceeds. The spermatid centrioles are long structures formed by nine doublet rather than triplet microtubules provided with short projections extending towards the surrounding cytoplasm and with links between doublets. The sperm basal bodies are aligned in parallel beneath the nucleus. They consist of long regions close to the nucleus showing nine doublets in a cartwheel array devoid of any projections; on the contrary, the short region close to the plasma membrane, where the sperm flagella emerge, is characterized by projections similar to those observed in the centrioles linking the basal body to the plasma membrane. It is hypothesized that this appearance is in connection with the centriole elongation and further with the flagellar axonemal organization. Microtubule doublets of sperm flagellar axonemes are provided with outer dynein arms, while inner arms are rarely visible. Cell Motil. Cytoskeleton 2009. © 2009 Wiley-Liss, Inc. [source] The ankyrin repeat as molecular architecture for protein recognitionPROTEIN SCIENCE, Issue 6 2004Leila K. Mosavi Abstract The ankyrin repeat is one of the most frequently observed amino acid motifs in protein databases. This protein,protein interaction module is involved in a diverse set of cellular functions, and consequently, defects in ankyrin repeat proteins have been found in a number of human diseases. Recent biophysical, crystallographic, and NMR studies have been used to measure the stability and define the various topological features of this motif in an effort to understand the structural basis of ankyrin repeat-mediated protein,protein interactions. Characterization of the folding and assembly pathways suggests that ankyrin repeat domains generally undergo a two-state folding transition despite their modular structure. Also, the large number of available sequences has allowed the ankyrin repeat to be used as a template for consensus-based protein design. Such projects have been successful in revealing positions responsible for structure and function in the ankyrin repeat as well as creating a potential universal scaffold for molecular recognition. [source] Determining the topology of virus assembly intermediates using ion mobility spectrometry,mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 20 2010Tom W. Knapman We have combined ion mobility spectrometry,mass spectrometry with tandem mass spectrometry to characterise large, non-covalently bound macromolecular complexes in terms of mass, shape (cross-sectional area) and stability (dissociation) in a single experiment. The results indicate that the quaternary architecture of a complex influences its residual shape following removal of a single subunit by collision-induced dissociation tandem mass spectrometry. Complexes whose subunits are bound to several neighbouring subunits to create a ring-like three-dimensional (3D) architecture undergo significant collapse upon dissociation. In contrast, subunits which have only a single neighbouring subunit within a complex retain much of their original shape upon complex dissociation. Specifically, we have determined the architecture of two transient, on-pathway intermediates observed during in vitro viral capsid assembly. Knowledge of the mass, stoichiometry and cross-sectional area of each viral assembly intermediate allowed us to model a range of potential structures based on the known X-ray structure of the coat protein building blocks. Comparing the cross-sectional areas of these potential architectures before and after dissociation provided tangible evidence for the assignment of the topologies of the complexes, which have been found to encompass both the 3-fold and the 5-fold symmetry axes of the final icosahedral viral shell. Such insights provide unique information about virus assembly pathways that could allow the design of anti-viral therapeutics directed at the assembly step. This methodology can be readily applied to the structural characterisation of many other non-covalently bound macromolecular complexes and their assembly pathways. Copyright © 2010 John Wiley & Sons, Ltd. [source] | |||||||||||||