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Despite SH2 domains, being pivotal in protein interactions linked to various diseases like cancer, we lack specific research tools for intracellular assays. Understanding SH2-mediated interactions and creating effective inhibitors requires tools which target individual protein domains. Affimer reagents exhibit promise, yet their potential against the extensive SH2 domain family remains largely unexplored. Our study aimed to bridge this gap by identifying Affimer reagents that selectively bind to 22 out of 41 SH2 domains. These reagents enabled a medium-throughput screening approach resembling siRNA studies, shedding light on their functionality. Notably, select Affimers demonstrated the ability to curtail the nuclear translocation of pERK, with Grb2 being a prominent target. Further analyses revealed that these Grb2-specific Affimer reagents displayed competitive inhibition with impressive metrics: IC50s ranging from 270.9 nM to 1.22 µM, together with low nanomolar binding affinities. Moreover, they exhibited the ability to pull down endogenous Grb2 from cell lysates, illustrating their efficacy in binding the Grb2 SH2 domain. This comprehensive assessment underscores the potential of Affimer reagents as domain-specific inhibitors. Their viability for medium/high-throughput phenotypic screening presents a promising avenue via which to identify and characterize potential drug targets within the SH2 domain family., Competing Interests: Declarations Competing interests MJ is an employee of Avacta Life Sciences and holds shares in the company, the Affimer technology is licensed to Avacta Life Sciences by the University of Leeds. The royalties from the license are managed by ULIP at the University of Leeds and disseminated to the inventors DCT and MJM. All other authors do not have a competing interest., (© 2024. The Author(s).)

Src homology 3 (SH3) domains play a critical role in mediating protein-protein interactions (PPIs) involved in cell proliferation, migration, and the cytoskeleton. Despite their abundance in the human proteome, the functions and molecular interactions of many SH3 domains remain unknown, and this is in part due to the lack of SH3-domain-specific reagents available for their study. Affimer proteins have been developed as affinity reagents targeting a diverse range of targets, including those involved in PPIs. In this study, Affimer proteins were isolated against both the N- and C-terminal SH3 domains (NSH3 and CSH3) of growth-factor-receptor-bound protein 2 (Grb2), an adapter protein that provides a critical link between cell surface receptors and Ras signalling pathways. Targeting the CSH3 alone for the inhibition of PPIs appeared sufficient for curtailing Ras signalling in mammalian cell lines stimulated with human epidermal growth factor (EGF), which conflicts with the notion that the predominant interactions with Ras activating Son of sevenless (SOS) occur via the NSH3 domain. This result supports a model in which allosteric mechanisms involved in Grb2-SOS1 interaction modulate Ras activation.

Dilated Cardiomyopathy is a common form of heart failure. Determining how this disease affects the structure and organization of cardiomyocytes in the human heart is important in understanding how the heart becomes less effective at contraction. Here we isolated and characterised Affimers (small non-antibody binding proteins) to Z-disc proteins ACTN2 (α-actinin-2), ZASP (also known as LIM domain binding protein 3 or LDB3) and the N-terminal region of the giant protein titin (TTN Z1-Z2). These proteins are known to localise in both the sarcomere Z-discs and the transitional junctions, found close to the intercalated discs that connect adjacent cardiomyocytes. We use cryosections of left ventricles from two patients diagnosed with end-stage Dilated Cardiomyopathy who underwent Orthotopic Heart Transplantation and were whole genome sequenced. We describe how Affimers substantially improve the resolution achieved by confocal and STED microscopy compared to conventional antibodies. We quantified the expression of ACTN2, ZASP and TTN proteins in two patients with dilated cardiomyopathy and compared them with a sex- and age-matched healthy donor. The small size of the Affimer reagents, combined with a small linkage error (the distance from the epitope to the dye label covalently bound to the Affimer) revealed new structural details in Z-discs and intercalated discs in the failing samples. Affimers are thus useful for analysis of changes to cardiomyocyte structure and organisation in diseased hearts., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Parker, Tang, Rogers, Carrington, dos Remedios, Li, Tomlinson and Peckham.)

Artificial binding proteins have been validated as alternatives to antibodies in their use as research reagents in molecular and cellular biology. For example, they have been used as inhibitors of protein-protein interactions to modulate activity, to facilitate crystallization, and as probes for cellular imaging.Phage display is a widely used approach for isolating target-specific binding reagents, and it has even been used to isolate isoform-specific binding proteins and binders that can distinguish between highly homologous protein domains.Here, we describe methods that have been employed in isolating highly specific artificial binding proteins against a wide range of target proteins.

Adhirons are robust, well expressing, peptide display scaffold proteins, developed as an effective alternative to traditional antibody binding proteins for highly specific molecular recognition applications. This paper reports for the first time the use of these versatile proteins for material binding, and as tools for controlling material synthesis on the nanoscale. A phage library of Adhirons, each displaying two variable binding loops, was screened to identify specific proteins able to interact with [100] faces of cubic magnetite nanoparticles. The selected variable regions display a strong preference for basic residues such as lysine. Molecular dynamics simulations of amino acid adsorption onto a [100] magnetite surface provides a rationale for these interactions, with the lowest adsorption energy observed with lysine. These proteins direct the shape of the forming nanoparticles towards a cubic morphology in room temperature magnetite precipitation reactions, in stark contrast to the high temperature, harsh reaction conditions currently used to produce cubic nanoparticles. These effects demonstrate the utility of the selected Adhirons as novel magnetite mineralization control agents using ambient aqueous conditions. The approach we outline with artificial protein scaffolds has the potential to develop into a toolkit of novel additives for wider nanomaterial fabrication.