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17 p.-8 fig.-1 tab., Allergic reactions to antibiotics are a major concern in the clinic. ß-lactam antibiotics are the class most frequently reported to cause hypersensitivity reactions. One of the mechanisms involved in this outcome is the modification of proteins by covalent binding of the drug (haptenation). Hence, interest in identifying the corresponding serum and cellular protein targets arises. Importantly, haptenation susceptibility and extent can be modulated by the context, including factors affecting protein conformation or the occurrence of other posttranslational modifications. We previously identified the glycolytic enzyme α-enolase as a target for haptenation by amoxicillin, both in cells and in the extracellular milieu. Here, we performed an in vitro study to analyze amoxicillin haptenation of α-enolase using gel-based and activity assays. Moreover, the possible interplay or interference between amoxicillin haptenation and acetylation of α-enolase was studied in 1D- and 2D-gels that showed decreased haptenation and displacement of the haptenation signal to lower pI spots after chemical acetylation of the protein, respectively. In addition, the peptide containing lysine 239 was identified by mass spectrometry as the amoxicillin target sequence on α-enolase, thus suggesting a selective haptenation under our conditions. The putative amoxicillin binding site and the surrounding interactions were investigated using the α-enolase crystal structure and molecular docking. Altogether, the results obtained provide the basis for the design of novel diagnostic tools or approaches in the study of amoxicillin-induced allergic reactions., This work was supported by grants from the Ministerio de Ciencia e Innovación cofunded by ERDF (SAF2015-68590-R and RTI2018-097624-B-I00 to DPS and PCI2019-111825-2 Proyectos de I+D+I “Programación Conjunta Internacional” EuroNanoMed 2019 and PID2019-104293GB-I00 to EI), the Instituto de Salud Carlos III ERDF (RETIC ARADyAL RD16/0006/0021 to DPS, RETIC ARADyAL RD16/0006/0001 to MS and MIM, CPII20/00028 to MIM and RETIC ARADyAL RD16/0006/0012 to EPI, and CPII20/00028 to MIM), Junta de Andalucía and Universidad de Málaga (UMA18-FEDERJA-007 to EPI), Consejería de Transformación Económica, Industria, Conocimiento y Universidades of Junta de Andalucía (PY20_00384 to EPI). The funders had no role in study design, analysis of the data or decission to publish. We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).

12 p.-6 fig.-1 graf. abst., BACKGROUND: Selective reactions to clavulanic acid (CLV) account for around 30% of immediate reactions after administration of amoxicillin-CLV. Currently, no immunoassay is available for detecting specific IgE to CLV, and its specific recognition in patients with immediate reactions has only been demonstrated by basophil activation testing, however with suboptimal sensitivity. The lack of knowledge regarding the structure of the drug that remains bound to proteins (antigenic determinant) is hampering the development of in vitro diagnostics. We aimed to identify the antigenic determinants of CLV as well as to evaluate their specific IgE recognition and potential role for diagnosis., METHODS: Based on complex CLV degradation mechanisms, we hypothesized the formation of two antigenic determinants for CLV, AD-I (N-protein, 3-oxopropanamide) and AD-II (N-protein, 3-aminopropanamide), and designed different synthetic analogs to each one. IgE recognition of these structures was evaluated in basophils from patients with selective reactions to CLV and tolerant subjects. In parallel, the CLV fragments bound to proteins were identified by proteomic approaches., RESULTS: Two synthetic analogs of AD-I were found to activate basophils from allergic patients. This determinant was also detected bound to lysines 195 and 475 of CLV-treated human serum albumin. One of these analogs was able to activate basophils in 59% of patients whereas CLV only in 41%. Combining both results led to an increase in basophil activation in 69% of patients, and only in 12% of controls., CONCLUSION: We have identified AD-I as one CLV antigenic determinant, which is the drug fragment that remains protein-bound., The present study has been supported by Institute of Health “Carlos III” of the Ministry of Economy and Competitiveness (grants cofunded by European Regional Development Fund (ERDF): PI12/02529, PI15/01206, CP15/00103, RETICs RIRAAF RD12/0013/0001, RD12/0013/0003 and RD12/0013/0008, RETIC ARADYAL RD16/0006/0001, RD16/0006/0012 and RD16/0006/0021, Biobank Network RD09/0076/00112, and Biobank platform PT13/0010/0006) and by State Secretariat for Research, Development and Innovation of the Ministry of Economy and Competitiveness (grants cofunded by European Regional Development Fund (ERDF), “Una manera de hacer Europa”: MINECO SAF2012-36519, SAF2015-68590R, CTQ2013-41339P, and CTQ2016-75870P). Andalusian Regional Ministry of Economy and Knowledge (grants cofunded by European Regional Development Fund (ERDF), “Andalucía se mueve con Europa”: CTS-06603); Andalusian Regional Ministry Health (grants: PI-0699-2011, PI-0159-2013, PI-0179-2014, PI-0241-2016, and PI-0250-2016), Merck-Serono Research Grant from Fundación Salud 2000 and “Premio UNICAJA a la innovación en biomedicina y salud.” CM holds a “Nicolas Monardes” research contract by Andalusian Regional Ministry Health: C-0044-2012 SAS 2013. MIM holds a “Miguel Servet I” and GB holds a “Rio Hortega,” both research contracts by Institute of Health “Carlos III” of the Ministry of Economy and Competitiveness (grants cofunded by European Social Fund (ESF)): CP15/00103 and CM16/00067. TDF hold a “Ramon y Cajal” research contract from Ministry of Economy and Competitiveness (RYC-2013-13138).