SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: The Assembly

70

We report the sequencing and assembly of a reference genome for the human GM12878 Utah/Ceph cell line using the MinION (Oxford Nanopore Technologies) nanopore sequencer. 91.2 Gb of sequence data, representing ∼30× theoretical coverage, were produced. Reference-based alignment enabled detection of large structural variants and epigenetic modifications. De novo assembly of nanopore reads alone yielded a contiguous assembly (NG50 ∼3 Mb). We developed a protocol to generate ultra-long reads (N50 > 100 kb, read lengths up to 882 kb). Incorporating an additional 5× coverage of these ultra-long reads more than doubled the assembly contiguity (NG50 ∼6.4 Mb). The final assembled genome was 2,867 million bases in size, covering 85.8% of the reference. Assembly accuracy, after incorporating complementary short-read sequencing data, exceeded 99.8%. Ultra-long reads enabled assembly and phasing of the 4-Mb major histocompatibility complex (MHC) locus in its entirety, measurement of telomere repeat length, and closure of gaps in the reference human genome assembly GRCh38.

Concepts: The Assembly, Cell, Base pair, Genetics, Human genome, Gene, Major histocompatibility complex, DNA

25

The success of polymer coatings for biomedical applications is undeniable. Among the very successful examples are poly(dopamine) (PDA) films due to their simplicity in deposition and beneficial interaction with biomolecules and cells. The aim of this review is to highlight the findings and achievement of PDA in nanomedicine since 2011. We discuss the progress that has been made to elucidate the structure of PDA and novel aspects considering the assembly of PDA-based films on diverse substrates. We highlight the newest results considering the biological evaluation PDA-based coatings to control cell behavior and the use of PDA in biosensing. The popularity of PDA remains unchanged, but the research efforts start to be consolidated toward more specific aims and clinical applications.

Concepts: Biomolecule, Cell, Enzyme, The Assembly, Success, Gene, DNA, Organism

23

Despite recent advances in the assembly of organic nanotubes, conferral of sequence-defined engineering and dynamic response characteristics to the tubules remains a challenge. Here we report a new family of highly designable and dynamic nanotubes assembled from sequence-defined peptoids through a unique “rolling-up and closure of nanosheet” mechanism. During the assembly process, amorphous spherical particles of amphiphilic peptoid oligomers crystallize to form well-defined nanosheets before folding to form single-walled nanotubes. These nanotubes undergo a pH-triggered, reversible contraction-expansion motion. By varying the number of hydrophobic residues of peptoids, we demonstrate tuning of nanotube wall thickness, diameter, and mechanical properties. Atomic force microscopy-based mechanical measurements show peptoid nanotubes are highly stiff (Young’s Modulus ~13-17 GPa). We further demonstrate the precise incorporation of functional groups within nanotubes and their applications in water decontamination and cellular adhesion and uptake. These nanotubes provide a robust platform for developing biomimetic materials tailored to specific applications.

Concepts: The Assembly, Pascal, Carbon nanotube, Stiffness, Functional group, Organic chemistry, Engineering, Young's modulus

19

The mammalian pseudokinase SgK223, and its structurally related homologue SgK269, are oncogenic scaffolds that nucleate the assembly of specific signalling complexes and regulate tyrosine kinase signalling. Both SgK223 and SgK269 form homo- and hetero-oligomers, a mechanism that underpins a diversity of signalling outputs. However, mechanistic insights into SgK223 and SgK269 homo- and heterotypic association are lacking. Here we present the crystal structure of SgK223 pseudokinase domain and its adjacent N- and C-terminal helices. The structure reveals how the N- and C-regulatory helices engage in a novel fold to mediate the assembly of a high-affinity dimer. In addition, we identified regulatory interfaces on the pseudokinase domain required for the self-assembly of large open-ended oligomers. This study highlights the diversity in how the kinase fold mediates non-catalytic functions and provides mechanistic insights into how the assembly of these two oncogenic scaffolds is achieved in order to regulate signalling output.

Concepts: Mechanism, The Assembly, Structure, Protein, User interface, Signal transduction, Monomer, Protein kinase

15

Peptoid nanosheets are a recently discovered class of 2D nanomaterial that form from the self-assembly of a sequence-specific peptoid polymer at an air-water interface. Nanosheet formation occurs first through the assembly of a peptoid monolayer and subsequent compression into a bilayer structure. These bilayer materials span hundreds of micrometers in lateral dimensions and have the potential to be used in a variety of applications, such as in molecular sensors, artificial membranes, and as catalysts. This paper reports that the oil-water interface provides another opportunity for growth of these unique and highly ordered peptoid sheets. The monolayers formed at this interface are found through surface spectroscopic measurements to be highly ordered and electrostatic interactions between the charged moieties, namely carboxylate and ammonium residues, of the peptoid are essential in the ability of these peptoids to form ordered nanosheets at the oil-water interface. Expanding the mechanism of peptoid nanosheet formation to the oil-water interface and understanding the crucial role of electrostatic interactions between peptoid residues in nanosheet formation is essential for increasing the complexity and functionality of these nanomaterials.

Concepts: Peptoid, Nanomaterials, The Assembly, Monolayer, Solid, Physical chemistry, Electric charge, Nanotechnology

12

Long-read sequencing technologies have potential to produce gold-standard de novo genome assemblies, but fully exploiting error-prone reads to resolve repeats remains a challenge. Aggressive approaches to repeat resolution often produce mis-assemblies, and conservative approaches lead to unnecessary fragmentation. We present HINGE, an assembler that achieves optimal repeat resolution by distinguishing repeats that can be resolved given the data from those that cannot. This is accomplished by adding “hinges” to reads for constructing an overlap graph where only unresolvable repeats are merged. As a result, HINGE combines the error resilience of overlap-based assemblers with repeat-resolution capabilities of de Bruijn graph assemblers. HINGE was evaluated on the long-read datasets from the NCTC project. Besides producing more finished assemblies than the manual pipeline of NCTC based on the HGAP assembler and Circlator, HINGE allows us to identify 40 datasets where unresolvable repeats prevent the reliable construction of a unique finished assembly. In these cases, HINGE outputs a visually interpretable assembly graph that encodes all possible finished assemblies consistent with the reads, while other approaches either fragment the assembly or resolve the ambiguity arbitrarily.

Concepts: Repeat sign, Fragmentation, Resolution, The Assembly, Nicolaas Govert de Bruijn, De Bruijn sequence, De Bruijn graph, Assembly language

7

Species and interactions are being lost at alarming rates and it is imperative to understand how communities assemble if we have to prevent their collapse and restore lost interactions. Using an 8-year dataset comprising nearly 20 000 pollinator visitation records, we explore the assembly of plant-pollinator communities at native plant restoration sites in an agricultural landscape. We find that species occupy highly dynamic network positions through time, causing the assembly process to be punctuated by major network reorganisations. The most persistent pollinator species are also the most variable in their network positions, contrary to what preferential attachment - the most widely studied theory of ecological network assembly - predicts. Instead, we suggest assembly occurs via an opportunistic attachment process. Our results contribute to our understanding of how communities assembly and how species interactions change through time while helping to inform efforts to reassemble robust communities.

Concepts: Understanding, The Assembly, C, Assembly language

6

An ability to develop sequence-defined synthetic polymers that both mimic lipid amphiphilicity for self-assembly of highly stable membrane-mimetic 2D nanomaterials and exhibit protein-like functionality would revolutionize the development of biomimetic membranes. Here we report the assembly of lipid-like peptoids into highly stable, crystalline, free-standing and self-repairing membrane-mimetic 2D nanomaterials through a facile crystallization process. Both experimental and molecular dynamics simulation results show that peptoids assemble into membranes through an anisotropic formation process. We further demonstrated the use of peptoid membranes as a robust platform to incorporate and pattern functional objects through large side-chain diversity and/or co-crystallization approaches. Similar to lipid membranes, peptoid membranes exhibit changes in thickness upon exposure to external stimuli; they can coat surfaces in single layers and self-repair. We anticipate that this new class of membrane-mimetic 2D nanomaterials will provide a robust matrix for development of biomimetic membranes tailored to specific applications.

Concepts: Assembly language, Polymer, The Assembly, Peptoid, Crystal, Molecular dynamics, Crystallization

6

Using DNA as programmable, sequence-specific ‘glues’, shape-controlled hydrogel units are self-assembled into prescribed structures. Here we report that aggregates are produced using hydrogel cubes with edge lengths ranging from 30 μm to 1 mm, demonstrating assembly across scales. In a simple one-pot agitation reaction, 25 dimers are constructed in parallel from 50 distinct hydrogel cube species, demonstrating highly multiplexed assembly. Using hydrogel cuboids displaying face-specific DNA glues, diverse structures are achieved in aqueous and in interfacial agitation systems. These include dimers, extended chains and open network structures in an aqueous system, and dimers, chains of fixed length, T-junctions and square shapes in the interfacial system, demonstrating the versatility of the assembly system.

Concepts: Tesseract, Length, The Assembly, Square, Units of measurement, Cube, Volume, Orders of magnitude

5

The assembly of Next Generation Sequencing (NGS) reads remains a challenging task. This is especially true for the assembly of metagenomics data that originate from environmental samples potentially containing hundreds to thousands of unique species. The principle objective of current assembly tools is to assemble NGS reads into contiguous stretches of sequence called contigs while maximizing for both accuracy and contig length. The end goal of this process is to produce longer contigs with the major focus being on assembly only. Sequence read assembly is an aggregative process, during which read overlap relationship information is lost as reads are merged into longer sequences or contigs. The assembly graph is information rich and capable of capturing the genomic architecture of an input read data set. We have developed a novel hybrid graph in which nodes represent sequence regions at different levels of granularity. This model, utilized in the assembly and analysis pipeline Focus, presents a concise yet feature rich view of a given input data set, allowing for the extraction of biologically relevant graph structures for graph mining purposes.

Concepts: Series, The Assembly, Genomics, Set, Star Trek: The Next Generation, Biology, Molecular biology, Sequence