Biology subjects

Harman, J. L.

Publications and source records attributed to Harman, J. L..

6 recordsLinked to original sources

bioRxiv2026

The Synthetic Epitope Atlas: High-Throughput Design and Validation of De Novo Antibody-Antigen Complexes

AO_SCPLOWBSTRACTC_SCPLOWDe novo antibody design models lack sufficient training data to reliably generalize. We demonstrate scalable generation of structural training data for machine learning-driven antibody design by linking in silico designs of antibody-antigen complexes to high-throughput experimental binding validation. Using AlphaSeq, a yeast-based platform for measuring protein binding affinities, we measure the affinity and specificity of thousands of de novo "synthetic epitope proteins" (SEPs) designed to bind to VHHs. The resulting Synthetic Epitope Atlas (SEPIA) pairs over 26 million on- and off-target affinity measurements with computationally designed VHH-SEP "pseudo-structures." We validate strong, specific binding for 1,161 pseudo-structures and >75,000 VHH and SEP mutational variants. We show that these pseudo-structures complement existing structural databases and enable ML models to outperform confidence metrics commonly used to rank de novo antibody designs. Taken together, SEPIA establishes a scalable framework for improving de novo antibody design by augmenting sparse structural data with large-scale experimental binding data.

synthetic biology↗

bioRxiv2025

LuxSit Pro and sPro: Next-Generation Designed Luciferases for Bioluminescent Reporting and Complementation-Based Detection

Bioluminescent systems are widely used as molecular reporters in life sciences due to their low background, broad dynamic range, and the key advantage of not requiring external excitation. However, natural luciferases often lack the brightness, stability, and long-lasting light emission needed to support a wide range of high-sensitivity applications. Here, we describe our next-generation luciferase solution: LuxSit Pro and its substrate, Luxterazine (LTZ). LuxSit Pro is a de novo luciferase optimized for steady brightness and structural stability through an iterative combination of computational and experimental methods. Composed of only 117 amino acids, LuxSit Pro is currently the smallest highest-performing known luciferase, exhibiting exceptional brightness and biochemical stability with robust recombinant expression in both mammalian and bacterial systems. Notably, LuxSit Pro was deliberately designed devoid of lysine and cysteine residues which enormously expands its potential applications. This property renders the reporter largely resistant to post-translational modifications such as ubiquitination and also enables site-directed chemical modifications, as lysines or cysteines can be reintroduced at specific sites to serve as chemical handles for augmenting or adapting the enzymes function. The novel synthetic substrate, Luxterazine (LTZ), is a compound that enables LuxSit Pro to deliver bright, steady, blue light emission ([~]490 nm) and offers improved solubility compared to existing Coelenterazine analogs. Finally, we also developed LuxSit sPro, a highly sensitive two-component complementation system for the quantitative detection of molecular interactions. The broad potential applications of LuxSit Pro and sPro, in combination with Luxterazine, are poised to drive the development of next-generation reporters and biosensor systems for the research and in vitro diagnostics fields.

molecular biology↗

bioRxiv2023

Macrophage-expressed Neuropilin 2 promotes plaque formation in ApoE knockout mice and is essential for pro-inflammatory macrophage polarisation and gene expression.

AimsAtherosclerosis is a chronic inflammatory disease causing the narrowing of arteries, leading to ischaemic heart disease. It is characterised by the subendothelial retention, and modification, of lipoproteins by macrophages, highly plastic cells which undergo polarisation to a pro-inflammatory phenotype in response to cytokines and other environmental stimuli. Neuropilin-2 (NRP2) is a cell-surface co-receptor with essential roles in angiogenesis and axonal guidance, that is also expressed by macrophages. However, the role of NRP2 in macrophage function in the development of atherosclerosis has not been studied. Methods and resultsThe role of NRP2 in modulating macrophage polarisation and signalling was assessed using functional assays and transcriptome analysis in macrophages obtained from mice with macrophage-specific deletion of Nrp2 (Nrp2-KOMac,EYFP). These mice were further crossed with pro-atherogenic Apolipoprotein E-deficient mice to produce Nrp2-KOMac,Apoe-/-,EYFP mice, which were fed a high-fat diet (HFD) for 16 weeks. Plaque formation and composition were characterised using chemical and immuno-staining. NRP2 was significantly upregulated upon differentiation of bone marrow progenitors into bone marrow derived macrophages (BMDM), and further upregulated by pro-inflammatory polarisation. Transcriptome analysis revealed that inflammatory signalling pathway genes, and genes regulating monocyte chemotaxis, were downregulated in Nrp2-KOMac,EYFP BMDMs. HFD-induced plaque development was significantly reduced in Nrp2-KOMac,Apoe-/-,EYFP mice. Additionally, plaques from those mice displayed features consistent with increased plaque stability, including reduced necrotic core area, plaque lipid content and increased cap thickness. ConclusionsMacrophage-derived NRP2 is proatherogenic, likely resulting from its ability to positively regulate pro-inflammatory pathways and macrophage migration. Targeting NRP2 expressed on the surface of macrophages could therefore offer a novel therapeutic approach for reducing the disease burden associated with atherosclerosis.

cell biology↗

bioRxiv2022

Evolution avoids a pathological stabilizing interaction in the immune protein S100A9

Stability constrains evolution. While much is known about constraints on destabilizing mutations, less is known about the constraints on stabilizing mutations. We recently identified a mutation in the innate immune protein S100A9 that provides insight into such constraints. When introduced into human S100A9, M63F simultaneously increases the stability of the protein and disrupts its natural ability to activate Toll-like receptor 4. Using chemical denaturation, we found that M63F stabilizes a calcium-bound conformation of hS100A9. We then used NMR to solve the structure of the mutant protein, revealing that the mutation distorts the hydrophobic binding surface of hS100A9, explaining its deleterious effect on function. Hydrogen deuterium exchange (HDX) experiments revealed stabilization of the region around M63F in the structure, notably Phe37. In the structure of the M63F mutant, the Phe37 and Phe63 sidechains are in contact, plausibly forming an edge-face {nu}-stack. Mutating Phe37 to Leu abolished the stabilizing effect of M63F as probed by both chemical denaturation and HDX. It also restored the biological activity of S100A9 disrupted by M63F. These findings reveal that Phe63 creates a "molecular staple" with Phe37 that stabilizes a non-functional conformation of the protein, thus disrupting function. Using a bioinformatic analysis, we found that S100A9 proteins from different organisms rarely have Phe at both positions 37 and 63, suggesting that avoiding a pathological stabilizing interaction indeed constrains S100A9 evolution. This work highlights an important evolutionary constraint on stabilizing mutations: they must avoid inappropriately stabilizing non-functional protein conformations. SIGNIFICANCE STATEMENTProtein stability constrains protein evolution. While much is known about evolutionary constraints on destabilizing mutations, less is known about the constraints on stabilizing mutations. We recently found a mutation to an innate immune protein that increases its stability but disrupts its function. Here we show, through careful biophysical and functional studies, that this mutation stabilizes a nonfunctional form of the protein through a direct interaction with another amino acid. We find that specific amino acids can be tolerated at each of the interacting positions individually, but not at both simultaneously. This pattern has been conserved over millions of years of evolution. Our work highlights an underappreciated evolutionary constraint on stabilizing mutations: they must avoid inappropriately stabilizing non-functional protein conformations.

biophysics↗

bioRxiv2020

Primed smooth muscle cells acting as first responder cells in disease

RationaleVascular smooth muscle cell (VSMC) dysregulation is a hallmark of vascular disease, including atherosclerosis. In particular, the majority of cells within atherosclerotic lesions are generated from pre-existing VSMCs and a clonal nature has been documented for VSMC-derived cells in multiple disease models. However, the mechanisms underlying the generation of oligoclonal lesions and the phenotype of proliferating VSMCs are unknown. ObjectiveTo understand the cellular mechanisms underlying clonal VSMC expansion in disease. Methods and ResultsHere we analyse clonal dynamics in multi-color lineage-traced animals over time after vessel injury. We demonstrate that VSMC proliferation is initiated in a small fraction of VSMCs that initially expand clonally in the medial layer and then migrate to form the oligoclonal neointima. Selective activation of VSMC proliferation also occurs in vitro, suggesting that this is a cell-autonomous feature. Mapping of VSMC trajectories using single-cell RNA-sequencing reveals a continuum of cellular states after injury and suggests that VSMC proliferation initiates in cells that have downregulated the contractile phenotype and show evidence of pronounced phenotypic switching. We show that proliferation is associated with induced expression of stem cell antigen 1 (SCA1) and the expression signature previously identified in SCA1+ VSMCs in healthy arteries. A remarkably increased proliferation of SCA1+ VSMCs, directly validated in functional assays, indicates that SCA1+ VSMCs act as "first responders" in vascular injury. Early atherosclerotic lesions also had clonal VSMC contribution and we show that the proliferation-associated injury response is conserved in plaque VSMCs, extending these findings to atherosclerosis. Finally, we identify VSMCs in healthy human arteries that correspond to the SCA1+ state in mouse VSMCs and show that genes identified as differentially expressed in this human VSMC subpopulation are enriched for genes showing genetic association with cardiovascular disease. ConclusionsWe show that cell-intrinsic, selective VSMC activation drives clonal proliferation after injury and in atherosclerosis. Our study suggests that healthy mouse and human arteries contain VSMCs characterised by expression of disease-associated genes that are predisposed for proliferation. Targeting such "first responder" cells in patients undergoing vascular surgery could effectively prevent injury-associated VSMC activation and neoatherosclerosis.

cell biology↗

bioRxiv2019

Evolution of multifunctionality through a pleiotropic substitution in the innate immune protein S100A9

Multifunctional proteins are evolutionary puzzles: how do proteins evolve to satisfy multiple functional constraints? S100A9 is one such multifunctional protein. It potently amplifies inflammation via Toll-like receptor 4 and is antimicrobial as part of a heterocomplex with S100A8. These two functions are seemingly regulated by proteolysis: S100A9 is readily degraded, while S100A8/S100A9 is resistant. We take an evolutionary biochemical approach to show that S100A9 evolved both functions and lost proteolytic resistance from a weakly proinflammatory, proteolytically resistant amniote ancestor. We identify a historical substitution that has pleiotropic effects on S100A9 proinflammatory activity and proteolytic resistance but has little effect on S100A8/S100A9 antimicrobial activity. We thus propose that mammals evolved S100A8/S100A9 antimicrobial and S100A9 proinflammatory activities concomitantly with a proteolytic "timer" to selectively regulate S100A9. This highlights how the same mutation can have pleiotropic effects on one functional state of a protein but not another, thus facilitating the evolution of multifunctionality.

biochemistry↗