Tip-to-tip interaction in the crystal packing of PACSIN 2 is important in regulating tubulation activity

Effects of Maternal Fiber Intake on Intestinal Morphology, Bacterial Profile and Proteome of Newborns Using Pig as Model

Dietary fiber intake during pregnancy may improve offspring intestinal development. The aim of this study was to evaluate the effect of maternal high fiber intake during late gestation on intestinal morphology, microbiota, and intestinal proteome of newborn piglets. Sixteen sows were randomly allocated into two groups receiving the control diet (CD) and high-fiber diet (HFD) from day 90 of gestation to farrowing. Newborn piglets were selected from each litter, named as CON and Fiber group, respectively. Maternal high fiber intake did not markedly improve the birth weight, but increased the body length, the ileal crypt depth and colonic acetate level. In addition, maternal high fiber intake increased the -diversity indices (Observed species, Simpson, and ACE), and the abundance of Acidobacteria and Bacteroidetes at phylum level, significantly increased the abundance of Bradyrhizobium and Phyllobacterium at genus level in the colon of newborn piglets. Moreover, maternal high fiber intake markedly altered the ileal proteome, increasing the abundances of proteins associated with oxidative status, energy metabolism, and immune and inflammatory responses, and decreasing abundances of proteins related to cellular apoptosis, cell structure, and motility. These findings indicated that maternal high fiber intake could alter intestinal morphology, along with the altered intestinal microbiota composition and proteome of offspring.

The intrinsically disordered region of the cytokinetic F-BAR protein Cdc15 performs a unique essential function in maintenance of cytokinetic ring integrity

Successful separation of two daughter cells (i.e., cytokinesis) is essential for life. Many eukaryotic cells divide using a contractile apparatus called the cytokinetic ring (CR) that associates dynamically with the plasma membrane (PM) and generates force that contributes to PM ingression between daughter cells. In Schizosaccharomyces pombe, important membrane-CR scaffolds include the paralogous F-BAR proteins Cdc15 and Imp2. Their conserved protein structure consists of the archetypal F-BAR domain linked to an SH3 domain by an intrinsically disordered region (IDR). Functions have been assigned to the F-BAR and SH3 domains. In this study we probed the function of the central IDR. We found that the IDR of Cdc15 is essential for viability and cannot be replaced by that of Imp2, whereas the F-BAR domain of Cdc15 can be swapped with several different F-BAR domains, including that of Imp2. Deleting part of the IDR results in CR defects and abolishes calcineurin phosphatase localization to the CR. Together these results indicate that Cdc15's IDR has a nonredundant essential function that coordinates regulation of CR architecture.

Curvature induction and sensing of the F-BAR protein Pacsin1 on lipid membranes via molecular dynamics simulations

F-Bin/Amphiphysin/Rvs (F-BAR) domain proteins play essential roles in biological processes that involve membrane remodelling, such as endocytosis and exocytosis. It has been shown that such proteins transform the lipid membrane into tubes. Notably, Pacsin1 from the Pacsin/Syndapin subfamily has the ability to transform the membrane into various morphologies: striated tubes, featureless wide and thin tubes, and pearling vesicles. The molecular mechanism of this interesting ability remains elusive. In this study, we performed all-atom (AA) and coarse-grained (CG) molecular dynamics simulations to investigate the curvature induction and sensing mechanisms of Pacsin1 on a membrane. From AA simulations, we show that Pacsin1 has internal structural flexibility. In CG simulations with parameters tuned from the AA simulations, spontaneous assembly of two Pacsin1 dimers through lateral interaction is observed. Based on the complex structure, we show that the regularly assembled Pacsin1 dimers bend a tensionless membrane. We also show that a single Pacsin1 dimer senses the membrane curvature, binding to a buckled membrane with a preferred curvature. These results provide molecular insights into polymorphic membrane remodelling.

Investigation of F-BAR domain PACSIN proteins uncovers membrane tubulation function in cilia assembly and transport

The intracellular ciliogenesis pathway requires membrane trafficking, fusion, and reorganization. Here, we demonstrate in human cells and zebrafish that the F-BAR domain containing proteins PACSIN1 and -2 play an essential role in ciliogenesis, similar to their binding partner and membrane reorganizer EHD1. In mature cilia, PACSINs and EHDs are dynamically localized to the ciliary pocket membrane (CPM) and transported away from this structure on membrane tubules along with proteins that exit the cilium. PACSINs function early in ciliogenesis at the ciliary vesicle (CV) stage to promote mother centriole to basal body transition. Remarkably, we show that PACSIN1 and EHD1 assemble membrane t7ubules from the developing intracellular cilium that attach to the plasma membrane, creating an extracellular membrane channel (EMC) to the outside of the cell. Together, our work uncovers a function for F-BAR proteins and membrane tubulation in ciliogenesis and explains how the intracellular cilium emerges from the cell.

Syndapin bridges the membrane-cytoskeleton divide during furrow extension

BAR domain proteins can regulate ‘membrane reservoirs’ that provide surface area and buffer membrane tension. Syndapin is an F-BAR and SH3 domain containing protein involved in cytoskeletal remodelling and endocytosis. The Syndapin F-BAR domain is uniquely versatile compared to others in the family and can bend phospholipid membranes into tubules of various diameters and directly bind actin. The Syndapin SH3 domain can also interact with actin remodelling proteins and modulate cytoskeletal contractility. Pseudocleavage furrow extension in the syncytial division cycles of Drosophila embryos requires the homeostatic control of conserved processes that control plasma membrane tension and actin contractility. We find that Syndapin plays an important role in promoting pseudocleavage furrow extension. We propose a model involving roles for Syndapin in membrane dynamics and direct or indirect effect on the cytoskeleton to explain how it affects pseudocleavage furrow growth, independent of its role in endocytosis.

Neuroproteomics and Systems Biology Approach to Identify Temporal Biomarker Changes Post Experimental Traumatic Brain Injury in Rats

Traumatic brain injury (TBI) represents a critical health problem of which diagnosis, management, and treatment remain challenging. TBI is a contributing factor in approximately one-third of all injury-related deaths in the United States. The Centers for Disease Control and Prevention estimate that 1.7 million people suffer a TBI in the United States annually. Efforts continue to focus on elucidating the complex molecular mechanisms underlying TBI pathophysiology and defining sensitive and specific biomarkers that can aid in improving patient management and care. Recently, the area of neuroproteomics–systems biology is proving to be a prominent tool in biomarker discovery for central nervous system injury and other neurological diseases. In this work, we employed the controlled cortical impact (CCI) model of experimental TBI in rat model to assess the temporal–global proteome changes after acute (1 day) and for the first time, subacute (7 days), post-injury time frame using the established cation–anion exchange chromatography-1D SDS gel electrophoresis LC–MS/MS platform for protein separation combined with discrete systems biology analyses to identify temporal biomarker changes related to this rat TBI model. Rather than focusing on any one individual molecular entity, we used in silico systems biology approach to understand the global dynamics that govern proteins that are differentially altered post-injury. In addition, gene ontology analysis of the proteomic data was conducted in order to categorize the proteins by molecular function, biological process, and cellular localization. Results show alterations in several proteins related to inflammatory responses and oxidative stress in both acute (1 day) and subacute (7 days) periods post-TBI. Moreover, results suggest a differential upregulation of neuroprotective proteins at 7 days post-CCI involved in cellular functions such as neurite growth, regeneration, and axonal guidance. Our study is among the first to assess temporal neuroproteome changes in the CCI model. Data presented here unveil potential neural biomarkers and therapeutic targets that could be used for diagnosis, for treatment and, most importantly, for temporal prognostic assessment following brain injury. Of interest, this work relies on in silico bioinformatics approach to draw its conclusion; further work is conducted for functional studies to validate and confirm the omics data obtained.

Structure of Dimeric and Tetrameric Complexes of the BAR Domain Protein PICK1 Determined by Small-Angle X-Ray Scattering

PICK1 is a neuronal scaffolding protein containing a PDZ domain and an auto-inhibited BAR domain. BAR domains are membrane-sculpting protein modules generating membrane curvature and promoting membrane fission. Previous data suggest that BAR domains are organized in lattice-like arrangements when stabilizing membranes but little is known about structural organization of BAR domains in solution. Through a small-angle X-ray scattering (SAXS) analysis, we determine the structure of dimeric and tetrameric complexes of PICK1 in solution. SAXS and biochemical data reveal a strong propensity of PICK1 to form higher-order structures, and SAXS analysis suggests an offset, parallel mode of BAR-BAR oligomerization. Furthermore, unlike accessory domains in other BAR domain proteins, the positioning of the PDZ domains is flexible, enabling PICK1 to perform long-range, dynamic scaffolding of membrane-associated proteins. Together with functional data, these structural findings are compatible with a model in which oligomerization governs auto-inhibition of BAR domain function.

FlnA binding to PACSIN2 F-BAR domain regulates membrane tubulation in megakaryocytes and platelets

Bin-Amphiphysin-Rvs (BAR) and Fes-CIP4 homology BAR (F-BAR) proteins generate tubular membrane invaginations reminiscent of the megakaryocyte (MK) demarcation membrane system (DMS), which provides membranes necessary for future platelets. The F-BAR protein PACSIN2 is one of the most abundant BAR/F-BAR proteins in platelets and the only one reported to interact with the cytoskeletal and scaffold protein filamin A (FlnA), an essential regulator of platelet formation and function. The FlnA-PACSIN2 interaction was therefore investigated in MKs and platelets. PACSIN2 associated with FlnA in human platelets. The interaction required FlnA immunoglobulin-like repeat 20 and the tip of PACSIN2 F-BAR domain and enhanced PACSIN2 F-BAR domain membrane tubulation in vitro. Most human and wild-type mouse platelets had 1 to 2 distinct PACSIN2 foci associated with cell membrane GPIbα, whereas Flna-null platelets had 0 to 4 or more foci. Endogenous PACSIN2 and transfected enhanced green fluorescent protein-PACSIN2 were concentrated in midstage wild-type mouse MKs in a well-defined invagination of the plasma membrane reminiscent of the initiating DMS and dispersed in the absence of FlnA binding. The DMS appeared less well defined, and platelet territories were not readily visualized in Flna-null MKs. We conclude that the FlnA-PACSIN2 interaction regulates membrane tubulation in MKs and platelets and likely contributes to DMS formation.

MICAL-L1-related and unrelated mechanisms underlying elongated tubular endosomal network (ETEN) in human dendritic cells

The endosomal pathway constitutes a highly dynamic intracellular transport system, which is composed of vesicular and tubular compartments. Endosomal tubules enable geometry-based discrimination between membrane and luminal content. Extended tubular endosomes were suggested to deliver a steady stream of membrane proteins to one location more reliable and effective than vesicular endosomes. Recently, we demonstrated that human dendritic cells (DCs) form a large elongated tubular endosomal network, e.g. ETEN, upon distinct triggers. LPS-stimulation triggered late endosomal tubulation. Additional clustering of class I MHC and ICAM-1 by a cognate interaction between antigen-laden DC and antigen-specific CD8⁺ T-cells induces formation of transferrin-positive tubules emanating from the endosomal recycling compartment (ERC). We here discuss cell-biological mechanisms that are involved in membrane bending and possibly underlie initiation, elongation, and stabilization of ETEN in human DCs. Using a knock-down approach we demonstrate that MICAL-L1 is necessary for ETEN remodeling originating from ERC in human DCs.