J.S.: funding acquisition. the CDR conformation. This study may inspire the rational design of artificial antibodies. Keywords: DNA nanotechnology, artificial antibody, complementary determining region, 5(6)-FITC conformation executive, antibody?antigen binding affinity Intro Creating artificial antibodies with customizable properties yet high affinity against specific focuses on is desirable for a wide range of applications, such as biomedicine, bioimaging, and intelligent theranostics.1,2 Antibodies are known to interact with antigens primarily through complementarity determining 5(6)-FITC areas (CDRs) within the variable areas.3 A CDR loop, typically comprising <20 amino acid residues, serves as the minimum motif to directly dictate the binding affinity with specific antigens through its amino acid sequence and 3D conformation.4,5 Thus, CDR engineering has emerged as a key focus in artificial antibody development.6?8 By grafting CDR loops onto engineered scaffold structures, one can modify the CDR conformation, resulting in complexes with altered properties, such as antigen binding affinity, specificity, and stability.9,10 For instance, the CDR conformation can be tuned by introducing site-directed mutagenesis in the scaffold proteins,11?14 but the design freedom is constrained by protein structural conservation. Recently, an indirect approach for tuning CDR conformation has been reported, which relies on grafting CDRs onto synthetic nanoparticles with different densities.15,16 A higher CDR density results in a shorter CDR span. However, the contribution of the CDR valency and CDR conformation to the antigen binding 5(6)-FITC affinity can hardly become decoupled. Moreover, the typical CDR loop span is definitely 1C2 nm, beyond the tuning resolution of most current synthetic materials. It is desired yet challenging to construct programmable scaffolds permitting independent rules of CDR conformation with a resolution at this size level.17 DNA nanotechnology, leveraging WatsonCCrick foundation pairing, allows for programmable design and synthesis of DNA nanostructures with exact sizes and shapes.18?20 These constructions, featuring B-form double-helix motifs with 2 nm diameter and 0.34 nm base pair spacing, provide scaffolds for moiety placement with subnanometer resolution.21?25 This precise addressability has led to the use of DNA nanostructures Mouse monoclonal to BLNK as frameworks to organize proteins such as antibodies,26,27 enzymes,28,29 or their subunits,30,31 enabling control over their quantities, combinations, interspaces, and orientations, thus regulating their activities and advertising biological applications.32?34 Here, we construct DNA framework based artificial antibodies (DNFbodies) with controlled CDR conformation by precisely dictating the anchoring range of the CDR loop terminals within the DNA frameworks with 2 nm resolution. We investigate the relationship between the CDR loop span and antigen binding affinity. We successfully reconstruct an optimized CDR conformation exhibiting a 3-fold increase in affinity compared to natural antibodies, efficiently inhibiting lysozyme activity and showcasing its potential for practical applications. Results and Conversation To reconstruct the CDR conformation, we used a double-crossover tile (DX tile) as the platform, known for its high rigidity.35,36 Camelid antilysosome antibody (cAb-Lys3), consisting solely of a heavy chain, was selected as the natural antibody to be transformed into a DNA framework based artificial antibody (DNFbody). Crystallographic analysis of the cAb-Lys3/HEWL (hen egg white lysozyme) complex revealed the N-terminal section of the CDR3 loop (comprising 100C112 amino acid residues) deeply stretches into the active-site crevice of lysozyme, making most of the antigen contacts37 (Number ?Figure11a). Consequently, we chose the 13 amino acid residues spanning approximately 1.4 nm in the binding state for CDR3 grafting (Number S1). In our experimental design, considering the structural stability of the DNA double helix and the interplay of complementary foundation pairing relationships,38,39 we devised terminal spacing at intervals of 0, 5, 11, and 21 nucleotides on DX tiles (Number ?Figure11b). The two ends of the CDR3 loop were anchored to these predetermined locations through covalent conjugation. Based on this, we carried out research within the reconstruction of DNFbodies with assorted CDR3 spans and their connection with antigens. Open in a separate window Number 1 Plan of the design of CDR grafting on DNA frameworks. (a) Structure of antibody cAb-Lys3 (gray, with the CDR3 loop demonstrated in reddish) in complex with HEWL (cyan) (Protein Data Standard bank (PDB) ID code 1JTP). (b) Building DNA framework centered artificial antibodies by anchoring a CDR3 loop revised with DBCO (dibenzocyclooctyne) and an amino group.