Broad neutralization of SARS-related viruses by human monoclonal antibodies

Broadly protective vaccines against known and preemergent human coronaviruses (HCoVs) are urgently needed. To gain a deeper understanding of cross-neutralizing antibody responses, we mined the memory B cell repertoire of a convalescent severe acute respiratory syndrome (SARS) donor and identified 200 SARS coronavirus 2 (SARS-CoV-2) binding antibodies that target multiple conserved sites on the spike (S) protein. A large proportion of the non-neutralizing antibodies display high levels of somatic hypermutation and cross-react with circulating HCoVs, suggesting recall of preexisting memory B cells elicited by prior HCoV infections. Several antibodies potently cross-neutralize SARS-CoV, SARS-CoV-2, and the bat SARS-like virus WIV1 by blocking receptor attachment and inducing S1 shedding. These antibodies represent promising candidates for therapeutic intervention and reveal a target for the rational design of pan-sarbecovirus vaccines

Specific roles of protein–phospholipid interactions in the yeast cytochrome bc(1) complex structure

Biochemical data have shown that specific, tightly bound phospholipids are essential for activity of the cytochrome bc(1) complex (QCR), an integral membrane protein of the respiratory chain. However, the structure and function of such phospholipids are not yet known. Here we describe five phospholipid molecules and one detergent molecule in the X-ray structure of yeast QCR at 2.3 Å resolution. Their individual binding sites suggest specific roles in facilitating structural and functional integrity of the enzyme. Interestingly, a phosphatidylinositol molecule is bound in an unusual interhelical position near the flexible linker region of the Rieske iron–sulfur protein. Two possible proton uptake pathways at the ubiquinone reduction site have been identified: the E/R and the CL/K pathway. Remarkably, cardiolipin is positioned at the entrance to the latter. We propose that cardiolipin ensures structural integrity of the proton-conducting protein environment and takes part directly in proton uptake. Site-directed mutagenesis of ligating residues confirmed the importance of the phosphatidylinositol- and cardiolipin-binding sites

N-Glycan Modification in Aspergillus Species▿

The production by filamentous fungi of therapeutic glycoproteins intended for use in mammals is held back by the inherent difference in protein N-glycosylation and by the inability of the fungal cell to modify proteins with mammalian glycosylation structures. Here, we report protein N-glycan engineering in two Aspergillus species. We functionally expressed in the fungal hosts heterologous chimeric fusion proteins containing different localization peptides and catalytic domains. This strategy allowed the isolation of a strain with a functional α-1,2-mannosidase producing increased amounts of N-glycans of the Man5GlcNAc2 type. This strain was further engineered by the introduction of a functional GlcNAc transferase I construct yielding GlcNAcMan5GlcNac2 N-glycans. Additionally, we deleted algC genes coding for an enzyme involved in an early step of the fungal glycosylation pathway yielding Man3GlcNAc2 N-glycans. This modification of fungal glycosylation is a step toward the ability to produce humanized complex N-glycans on therapeutic proteins in filamentous fungi

Assessing the binding properties of the anti-PD-1 antibody landscape using label-free biosensors.

Here we describe an industry-wide collaboration aimed at assessing the binding properties of a comprehensive panel of monoclonal antibodies (mAbs) against programmed cell death protein 1 (PD-1), an important checkpoint protein in cancer immunotherapy and validated therapeutic target, with well over thirty unique mAbs either in clinical development or market-approved in the United States, the European Union or China. The binding kinetics of the PD-1/mAb interactions were measured by surface plasmon resonance (SPR) using a Carterra LSA instrument and the results were compared to data collected on a Biacore 8K. The effect of chip type on the SPR-derived binding rate constants and affinities were explored and the results compared with solution affinities from Meso Scale Discovery (MSD) and Kinetic Exclusion Assay (KinExA) experiments. When using flat chip types, the LSA and 8K platforms yielded near-identical kinetic rate and affinity constants that matched solution phase values more closely than those produced on 3D-hydrogels. Of the anti-PD-1 mAbs tested, which included a portion of those known to be in clinical development or approved, the affinities spanned from single digit picomolar to nearly 425 nM, challenging the dynamic range of our methods. The LSA instrument was also used to perform epitope binning and ligand competition studies which revealed over ten unique competitive binding profiles within this group of mAbs

Characterization of the Pichia pastoris protein-O-mannosyltransferase gene family.

The methylotrophic yeast, Pichiapastoris, is an important organism used for the production of therapeutic proteins. However, the presence of fungal-like glycans, either N-linked or O-linked, can elicit an immune response or enable the expressed protein to bind to mannose receptors, thus reducing their efficacy. Previously we have reported the elimination of β-linked glycans in this organism. In the current report we have focused on reducing the O-linked mannose content of proteins produced in P. pastoris, thereby reducing the potential to bind to mannose receptors. The initial step in the synthesis of O-linked glycans in P. pastoris is the transfer of mannose from dolichol-phosphomannose to a target protein in the yeast secretory pathway by members of the protein-O-mannosyltransferase (PMT) family. In this report we identify and characterize the members of the P. pastoris PMT family. Like Candida albicans, P. pastoris has five PMT genes. Based on sequence homology, these PMTs can be grouped into three sub-families, with both PMT1 and PMT2 sub-families possessing two members each (PMT1 and PMT5, and PMT2 and PMT6, respectively). The remaining sub-family, PMT4, has only one member (PMT4). Through gene knockouts we show that PMT1 and PMT2 each play a significant role in O-glycosylation. Both, by gene knockouts and the use of Pmt inhibitors we were able to significantly reduce not only the degree of O-mannosylation, but also the chain-length of these glycans. Taken together, this reduction of O-glycosylation represents an important step forward in developing the P. pastoris platform as a suitable system for the production of therapeutic glycoproteins

Longitudinal dynamics of the human B cell response to the yellow fever 17D vaccine

A comprehensive understanding of the development and evolution of human B cell responses duced by pathogen exposure will facilitate the design of next-generation vaccines. Here, we utilized a gh-throughput single B cell cloning technology to longitudinally track the human B cell response to the llow fever virus 17D (YFV-17D) vaccine. The earlymemory B cell (MBC) response was mediated by both assical immunoglobulin M (IgM) (IgM(+)CD27(+)) and switched immunoglobulin (swIg(+)) MBC pulations; however, classical IgM MBCs waned rapidly, whereas swIg(+) and atypical IgM(+) and IgD(+) MBCs were stable over time. Affinity maturation continued for 6 to 9 mo following vaccination, providing evidence for the persistence of germinal center activity long after the period of active viral replication in peripheral blood. Finally, a substantial fraction of the neutralizing antibody response was mediated by public clones that recognize a fusion loop-proximal antigenic site within domain II of the viral envelope glycoprotein. Overall, our findings provide a framework for understanding the dynamics and complexity of human B cell responses elicited by infection and vaccination

Inhibitor sensitivity of <i>PMT</i> knockouts.

<p>For dilution assays, yeast cells were grown overnight in YSD and then adjusted to an OD600 of 1.0 using YSD, diluted in 10-fold increments, and then 3 µl of each dilution were spotted onto solid YSD media with varying concentrations of PMTi-3. The picture of the plate without PMTi-3 was taken after 48 hours, and the picture of the plates containing PMTi-3 were taken after 96 hours of incubation at 25^°C. YGLY4140 is the parent strain of YGLY6001 and YGLY4329, YGLY733 is the parent strain of YGLY3773 and YGLY5968, and NRRL -Y11430 is the parent strain of YGLY35032.</p

Western blot analysis of an IgG1 expressed in the presence of PMTi-3.

<p>The <i>PMT</i> wild type strain YGLY4280 was grown in 96 well deep-well plates and induced in medium containing no PMTi-3 (C) or increasing concentrations of PMTi-3 (0.0187, 0.0375, 0.075, 0.15, 0.3, 0.625, 1.25, 2.5, 5, 10 µg/ml). After overnight induction, 7 µl of each supernatant was separated by polyacrylamide gel electrophoresis (SDS-PAGE) and then electroblotted onto nitrocellulose membranes. IgG1 was detected using an anti-human IgG (heavy and light chain) antibody. Hyperglycosylated heavy-chain (indicated by an asterisk) is barely detectable at PMTi-3 concentrations of 0.15 µg/ml and higher, however strain growth and fitness (strain lysis) was still unaffected at PMTi-3 concentrations of up to 1.25 µg/ml. A representation of the PMTi-3 increase in concentration and the relative reduction in cell fitness are illustrated by <i>light</i> and <i>dark gray triangles</i> respectively.</p