HLA-DM Mediates Epitope Selection by a “Compare-Exchange” Mechanism when a Potential Peptide Pool Is Available

BACKGROUND: HLA-DM (DM) mediates exchange of peptides bound to MHC class II (MHCII) during the epitope selection process. Although DM has been shown to have two activities, peptide release and MHC class II refolding, a clear characterization of the mechanism by which DM facilitates peptide exchange has remained elusive. METHODOLOGY/PRINCIPAL FINDINGS: We have previously demonstrated that peptide binding to and dissociation from MHCII in the absence of DM are cooperative processes, likely related to conformational changes in the peptide-MHCII complex. Here we show that DM promotes peptide release by a non-cooperative process, whereas it enhances cooperative folding of the exchange peptide. Through electron paramagnetic resonance (EPR) and fluorescence polarization (FP) we show that DM releases prebound peptide very poorly in the absence of a candidate peptide for the exchange process. The affinity and concentration of the candidate peptide are also important for the release of the prebound peptide. Increased fluorescence energy transfer between the prebound and exchange peptides in the presence of DM is evidence for a tetramolecular complex which resolves in favor of the peptide that has superior folding properties. CONCLUSION/SIGNIFICANCE: This study shows that both the peptide releasing activity on loaded MHCII and the facilitating of MHCII binding by a candidate exchange peptide are integral to DM mediated epitope selection. The exchange process is initiated only in the presence of candidate peptides, avoiding possible release of a prebound peptide and loss of a potential epitope. In a tetramolecular transitional complex, the candidate peptides are checked for their ability to replace the pre-bound peptide with a geometry that allows the rebinding of the original peptide. Thus, DM promotes a "compare-exchange" sorting algorithm on an available peptide pool. Such a "third party"-mediated mechanism may be generally applicable for diverse ligand recognition in other biological systems

Development and characterization of Pleurotus ostreatus mushroomwheat bread

The Pleurotus ostreatus mushroom is a source of high nutritional value and bioactive compounds such as -glucans, with immunomodulatory, hypoglycemic and prebiotic activity. The aim of this work was to developed a bread with P. ostreatus powder (POP) to increase its nutritional value and reduce its glycemic index. Four formulations were proposed substituting 5, 10, 15 and 20\% of wheat flour (w/w) for POP in the bread and their physical characteristics and nutritional were evaluated. In addition to determining the glycemic index and the in vitro digestion of starch in the proposed formulations. Results shown that with the addition of POP the specific volume of the bread decreased, and it became darker. The nutritional value of the bread was enriched, since the content on proteins, fiber and minerals increased. The results of in vitro simulated gastrointestinal digestion demonstrated that bread supplemented with POP showed more optimal starch digestibility with slower digestion rate, lower eGI and RDS contents, which could bring health benefits to humans. These findings suggest that the mushroom powder is an excellent alternative to produce bread with improved nutritional quality and decreased glycemic index. This article is protected by copyright. All rights reservedThis work was financed by the National Council of Science and Technology (CONACYT) Mexico through the institutional program CONACYT-S923148. This study was also supported by the Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469/2019 unit and BioTecNorte operation(NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020 - Programa Operacional Regional do Norte and the Project ColOsH PTDC/BTM-SAL/30071/2017 (POCI-01-0145-FEDER-030071).info:eu-repo/semantics/publishedVersio