Biology subjects

Roberts, A. D.

Publications and source records attributed to Roberts, A. D..

4 recordsLinked to original sources

bioRxiv2026

Clathrin recruitment and assembly of phosphorylated B cell receptor is impaired in human diffuse large B cell lymphoma

The B cell receptor (BCR) drives the differentiation of naive B cells into activated plasma cells that produce antibodies. The BCR consists of a plasma membrane-bound surface immunoglobulin (sIg) that binds antigens, and two coreceptor subunits CD79A and CD79B. The intracellular domains of CD79A and CD79B initiate immune signaling and endocytosis of the receptor in healthy B cells. In diffuse large B cell lymphoma (DLBCL), an aggressive form of human blood cancer, the activated B cell like (ABC) subtype exhibits constitutive signaling that drives survival and proliferation. Here, in a model of human ABC DLBCL, we determine the localization of BCR components relative to plasma membrane structures using correlative super-resolution light and platinum replica transmission electron microscopy. We find that spontaneous clusters of the surface Immunoglobulin common to ABC lymphoma localize to smooth raised membrane domains. These structures are involved in the endocytosis of large receptor clusters. Surprisingly, activated phosphorylated CD79A (pCD79A) shows little colocalization with clathrin on or off smooth raised membranes. Furthermore, pCD79A spatially segregates away from both the slg and CD79B subunits of the BCR complex. A similar distribution was found for downstream phosphorylated Src family kinases. We propose that a disengagement of pCD79A away from sIg and CD79B allows the receptor to evade down-regulation through endocytosis and maintains signaling at the plasma membrane. This mechanism could drive aberrant signaling and the proliferation of lymphomas leading to disease.

cell biology↗

bioRxiv2020

The structure and spontaneous curvature of clathrin lattices at the plasma membrane.

Clathrin mediated endocytosis is the primary pathway for receptor and cargo internalization in eukaryotic cells. It is characterized by a polyhedral clathrin lattice that coats budding membranes. The mechanism and control of lattice assembly, curvature, and vesicle formation at the plasma membrane has been a matter of longstanding debate. Here, we use platinum replica and cryo electron microscopy and tomography to present a global structural framework of the pathway. We determine the shape and size parameters common to clathrin-mediated endocytosis. We show that clathrin sites maintain a constant surface area during curvature across multiple cell lines. Flat clathrin is present in all cells and spontaneously curves into coated pits without additional energy sources or recruited factors. Finally, we attribute curvature generation to loosely connected and pentagon-containing flat lattices that can rapidly curve when a flattening force is released. Together, these data present a new universal mechanistic model of clathrin-mediated endocytosis.

cell biology↗

bioRxiv2020

Design and fabrication of recombinant reflectin-based Bragg reflectors: bio-design engineering and photoisomerism induced wavelength modulation

The remarkable camouflage capabilities of cephalopods have inspired many to develop dynamic optical materials which exploit certain design principles and/or material properties from cephalopod dermal cells. Here, the angle-dependent optical properties of various single-layer reflectin thin-films are characterized within the UV-Vis-NIR regions. Following this, the design and fabrication of the first bio-inspired reflectin-based Bragg reflector is described, which was found to conserve the optical properties of single layer films but exhibit a unique characteristic; reduced angle-dependent reflectivity. Finally, a novel method of controlling reflectin thin-film optical properties is introduced; visible light-induced photoisomerism, representing a new class of reflectin-based optical materials.

synthetic biology↗

bioRxiv2018

Structurally distinct endocytic pathways for B cell receptors in B lymphocytes

B lymphocytes play a critical role in adaptive immunity. Upon antigen binding, B cell receptors (BCR) cluster on the plasma membrane and are internalized by endocytosis. In this process, B cells capture diverse antigens in various contexts and concentrations. However, it is unclear whether the mechanism of BCR endocytosis changes in response to these factors. Here, we studied the mechanism of soluble antigen-induced BCR clustering and internalization in a cultured human B cell line using correlative super resolution fluorescence and platinum replica electron microscopy. First, by visualizing nanoscale BCR clusters, we provide direct evidence that BCR cluster size increases with F(ab)2 concentration. Next, we show that the physical mechanism of internalization switches in response to BCR cluster size. At low concentrations of antigen, B cells internalize small BCR clusters by classical clathrin-mediated endocytosis. At high antigen concentrations, when clusters size increases beyond the size of a single clathrin coated pit, B cells retrieve receptor clusters using large invaginations of the plasma membrane capped with clathrin. At these sites, we observed early and sustained recruitment of actin and an actin polymerizing protein FCHSD2. We further show that actin recruitment is required for the efficient generation of these novel endocytic carriers and for their capture into the cytosol. We propose that in B cells, the mechanism of endocytosis switches to accommodate large receptor clusters formed when cells encounter high concentrations of soluble antigen. This mechanism is regulated by the organization and dynamics of the cortical actin cytoskeleton.

cell biology↗