Biology subjects

Saltukoglu, D.

Publications and source records attributed to Saltukoglu, D..

3 recordsLinked to original sources

bioRxiv2022

Structural principles of B-cell antigen receptor assembly

The B-cell antigen receptor (BCR) is composed of a membrane-bound immunoglobulin (mIg) of class M, D, G, A or E for antigen recognition and a disulfide-linked heterodimer between Ig and Ig{beta} (Ig/{beta}, also known as CD79A and CD79B) that functions as the signalling entity. The organizing principle of BCR assembly remains elusive. Here we report the cryo-electron microscopy structures of the intact IgM class BCR at 8.2 [A] resolution and its Fab-deleted form (IgM BCR{Delta}Fab) at 3.6 [A] resolution. At the ectodomain (ECD), Ig and Ig{beta} position their respective Ig folds roughly in parallel with an approximate 2-fold symmetry, which is distinct from structures of Ig{beta}/{beta} homodimers. Unlike previous predictions, the BCR structure displays an asymmetric arrangement, in which the Ig/{beta} ECD heterodimer mainly uses Ig to associate with C{micro}3-C{micro}4 domains of one heavy chain ({micro}HC) while leaving the other heavy chain ({micro}HC) empty. The transmembrane domain (TMD) helices of the two {micro}HCs also deviate from the 2-fold symmetry of the C{micro}3-C{micro}4 domain dimer and form together with the TMD helices of the Ig/{beta} heterodimer a tight 4-helix bundle. The asymmetry at the TMD helices prevents the recruitment of two Ig/{beta} heterodimers. Surprisingly, the connecting peptides (CPs) between the ECD and TMD are braided together through striking charge complementarity, resulting in intervening of the CP of {micro}HC in between those of Ig and Ig{beta} and crossover of the TMD relative to ECD for the Ig/{beta} heterodimer, to guide the TMD assembly. Interfacial analyses suggest that the IgM BCR structure we present here may represent a general organizational architecture of all BCR classes. Our studies thus provide a structural platform for understanding B-cell signalling and for designing rational therapies against BCR-mediated diseases.

immunology↗

bioRxiv2022

Plasma membrane topography governs the three-dimensional dynamic localization of IgM B cell receptor clusters

B lymphocytes recognize bacterial or viral antigens via different classes of the B cell antigen receptor (BCR). Protrusive structures termed microvilli cover lymphocyte surfaces and are thought to perform sensory functions in screening antigen-bearing surfaces. Here, we have studied the cell surface features of Ramos B cells and the spatiotemporal organization of the IgM-BCR using lattice light sheet microscopy in combination with tailored custom-built 4D image analysis. Ramos B cell surfaces were found to form dynamic networks of elevated ridges bridging individual microvilli. A proportion of membrane-localized IgM-BCR was found in clusters, which were associated with the ridges and the microvilli. The dynamic ridge network organization and the IgM-BCR cluster mobility were linked and both were controlled by Arp2/3 complex activity. Our results suggest that topographical features of the cell surface govern the distribution and dynamic localization of IgM-BCR clusters to facilitate antigen screening.

cell biology↗

bioRxiv2021

Engineered chimeric T cell receptor fusion construct (TRuC)-expressing T cells prevent translational shutdown in SARS-CoV-2-infected cells

SARS-CoV-2, the causative agent of Covid-19, is known to evade the immune system by several mechanisms. This includes the shutdown of the host cellular protein synthesis, which abrogates the induction of antiviral interferon responses. The virus initiates the infection of susceptible cells by binding with its spike protein (S) to the host angiotensin-converting enzyme 2 (ACE2). Here we applied the T cell receptor fusion construct (TRuC) technology to engineer T cells against such infected cells. In our TRuCs an S-binding domain is fused to the CD3{varepsilon} component of the T cell receptor (TCR) complex, enabling recognition of S-containing cells in an HLA independent manner. This domain either consists of the S-binding part of ACE2 or a single-chain variable fragment of an anti-S antibody. We show that the TRuC T cells are activated by and kill cells that express S of SARS-CoV-2 and its alpha (B.1.1.7) and beta (B.1.351) variants at the cell surface. Treatment of SARS-CoV-2 infected cells with our engineered T cells did not lead to massive cytotoxicity towards the infected cells, but resulted in a complete rescue of the translational shutdown despite ongoing viral replication. Our data show that engineered TRuC T cell products might be used against SARS-CoV-2 by exposing infected cells to the host innate immune system.

bioengineering↗