Proteins are designed to bind to specific surfaces while also presenting a programmed surface superstructure. There is a general need for the engineering of protein-like molecules that organize into geometrically specific superstructures on molecular surfaces, directing further functionalization to create richly textured, multilayered assemblies. Here we describe a computational approach whereby the surface properties and symmetry of a targeted surface define the sequence and superstructure of surface-organizing peptides. Computational design proceeds in a series of steps that encode both surface recognition and favorable intersubunit packing interactions. This procedure is exemplified in the design of peptides that assemble into a tubular structure surrounding single-walled carbon nanotubes (SWNTs). The geometrically defined, virus-like coating created by these peptides converts the smooth surfaces of SWNTs into highly textured assemblies with long-scale order, capable of directing the assembly of gold nanoparticles into helical arrays along the SWNT axis.

Computational Design of Virus-Like Protein Assemblies on Carbon

Fundamental processes influencing human growth can be revealed by studying extreme short stature. Using genetic linkage analysis, we find that biallelic loss-of-function mutations in the centrosomal pericentrin (PCNT) gene on chromosome 21q22.3 cause microcephalic osteodysplastic primordial dwarfism type II (MOPD II) in 25 patients. Adults with this rare inherited condition have an average height of 100 centimeters and a brain size comparable to that of a 3-month-old baby, but are of near-normal intelligence. Absence of PCNT results in disorganized mitotic spindles and missegregation of chromosomes. Mutations in related genes are known to cause primary microcephaly (MCPH1, CDK5RAP2, ASPM, and CENPJ).

Mutations in the epricentrin (PCNT) gene cause primordial dwarfism

Abstract Biological phase separation forming membraneless organelles in cytoplasm and nucleus has attracted considerable attention. Liquid-like condensates are often created as spherical droplets. However, various condensates with network-like morphologies, including protein granules, localisation bodies, and centrosome assemblies, have recently been discovered in cells. Therefore, what controls the morphology of biological phase separation is a critical issue but remains elusive. Here, based on the knowledge of viscoelastic phase separation in soft matter physics, we propose that the difference in the molecular dynamics between the two phases controls the condensate morphology. Small and large mobility differences between the two phases should lead to droplet-like and network-like morphologies of the minority phase, respectively. We show that asymmetric partitioning of high-molecular-weight unstructured polymers (e.g., messenger RNA) between the two phases increases the dynamic asymmetry between the phases to form a network-like pattern of the slower phase, which may further be stabilised through inter-polymer binding. 

https://www.nature.com/articles/s42005-022-00947-7.pdf

Viscoelastic phase separation in biological cells

Cells spatially organize their molecular components to carry out fundamental biological processes and guide proper development. The spatial organization of RNA within the cell can both promote and result from gene expression regulatory control. Recent studies have demonstrated diverse associations between RNA spatial patterning and translation regulatory control. One form of patterning, compartmentalization in biomolecular condensates, has been of particular interest. Generally, transcripts associated with cytoplasmic biomolecular condensates—such as germ granules, stress granules, and P-bodies—are linked with low translational status. However, recent studies have identified new biomolecular condensates with diverse roles associated with active translation. This review outlines RNA compartmentalization in various condensates that occur in association with repressed or active translational states, highlights recent findings in well-studied condensates, and explores novel condensate behaviors.

/pdf/its-just-a-phase-exploring-the-relationship-between-mrna-2vc6y64c.pdf

It’s Just a Phase: Exploring the Relationship Between mRNA, Biomolecular Condensates, and Translational Control

The 14-3-3 family proteins are vital scaffold proteins that ubiquitously expressed in various tissues. They interact with numerous protein targets and mediate many cellular signaling pathways. The 14-3-3 binding motifs are often embedded in intrinsically disordered regions which are closely associated with liquid–liquid phase separation (LLPS). In the past ten years, LLPS has been observed for a variety of proteins and biological processes, indicating that LLPS plays a fundamental role in the formation of membraneless organelles and cellular condensates. While extensive investigations have been performed on 14-3-3 proteins, its involvement in LLPS is overlooked. To date, 14-3-3 proteins have not been reported to undergo LLPS alone or regulate LLPS of their binding partners. To reveal the potential involvement of 14-3-3 proteins in LLPS, in this review, we summarized the LLPS propensity of 14-3-3 binding partners and found that about one half of them may undergo LLPS spontaneously. We further analyzed the phase separation behavior of representative 14-3-3 binders and discussed how 14-3-3 proteins may be involved. By modulating the conformation and valence of interactions and recruiting other molecules, we speculate that 14-3-3 proteins can efficiently regulate the functions of their targets in the context of LLPS. Considering the critical roles of 14-3-3 proteins, there is an urgent need for investigating the involvement of 14-3-3 proteins in the phase separation process of their targets and the underling mechanisms. 

/pdf/14-3-3-proteins-are-potential-regulators-of-liquid-liquid-8930y7nq.pdf

14-3-3 Proteins are Potential Regulators of Liquid–Liquid Phase Separation

At the onset of mitosis, centrosomes expand the pericentriolar material (PCM) to maximize their microtubule-organizing activity. This step, termed centrosome maturation, ensures proper spindle organization and faithful chromosome segregation. However, as the centrosome expands, how PCM proteins are recruited and held together without membrane enclosure remains elusive. We found that endogenously expressed pericentrin (PCNT), a conserved PCM scaffold protein, condenses into dynamic granules during late G2/early mitosis before incorporating into mitotic centrosomes. Furthermore, the N-terminal portion of PCNT, enriched with conserved coiled-coils (CCs) and low-complexity regions (LCRs), phase separates into dynamic condensates that selectively recruit PCM proteins and nucleate microtubules in cells. We propose that CCs and LCRs, two prevalent sequence features in the centrosomal proteome, are preserved under evolutionary pressure in part to mediate liquid-liquid phase separation, a process that bestows upon the centrosome distinct properties critical for its assembly and functions.

Condensation of pericentrin proteins in human cells illuminates phase separation in centrosome assembly

Mitotic centrosomes are complex membraneless organelles that guide the formation of mitotic spindles to ensure faithful cell division. They are formed by timely expansion of the pericentriolar material (PCM) around the centrioles at the onset of mitosis. How PCM proteins are recruited and held together without a lipid membrane remains elusive. Here we found that endogenously expressed pericentrin (PCNT), a conserved PCM scaffold protein, condenses into liquid-like granules during early mitosis in cultured human cells. Furthermore, the N-terminal segment of PCNT, enriched with conserved coiled-coils and low-complexity regions (LCRs), undergoes phase separation. These PCNT 9condensates9 selectively recruit PCM components and nucleate microtubules in cells. We propose that coiled-coils and LCRs, two prevalent sequence features in the centrosomal proteome, are preserved under evolutionary pressure to drive phase separation, a process that bestows upon the centrosome a distinct material property critical for its assembly and functions.

/pdf/condensation-of-pericentrin-proteins-in-human-cells-3sigdcj3t7.pdf

Dac Bang Tam Ho

Papers

Condensation of pericentrin proteins in human cells illuminates phase separation in centrosome assembly

Condensation of pericentrin proteins in human cells illuminates phase separation in centrosome assembly