{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,28]],"date-time":"2026-08-28T16:06:29Z","timestamp":1787933189914,"version":"build-2784847793"},"reference-count":54,"publisher":"SAGE Publications","issue":"5-6","license":[{"start":{"date-parts":[[2023,5,31]],"date-time":"2023-05-31T00:00:00Z","timestamp":1685491200000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/journals.sagepub.com\/page\/policies\/text-and-data-mining-license"}],"funder":[{"name":"Deutscher Akademischer Austausch Dienst","award":["91566064"],"award-info":[{"award-number":["91566064"]}]}],"content-domain":{"domain":["journals.sagepub.com"],"crossmark-restriction":true},"short-container-title":["Eur J Mass Spectrom (Chichester)"],"published-print":{"date-parts":[[2023,12]]},"abstract":"<jats:p>\n                    Pepsin, because of its optimal activity at low acidic pH, has gained importance in mass spectrometric proteome research as a readily available and easy-to-handle protease. Pepsin has also been study object of protein higher-order structure analyses, but questions about how to best investigate pepsin in-solution conformers still remain. We first determined dependencies of pepsin ion charge structures on solvent pH which indicated the in-solution existence of (a) natively folded pepsin (N) which by nanoESI-MS analysis gave rise to a narrow charge state distribution with an 11-fold protonated most intense ion signal, (b) unfolded pepsin (U) with a rather broad ion charge state distribution whose highest ion signal carried 25 protons, and (c) a compactly folded pepsin conformer (C) with a narrow charge structure and a 12-fold protonated ion signal in the center of its charge state envelope. Because pepsin is a protease, unfolded pepsin became its own substrate in solution at pH 6.6 since at this pH some portion of pepsin maintained a compact\/native fold which displayed enzymatic activity. Subsequent mass spectrometric ITEM-TWO analyses of pepstatin A \u2013 pepsin complex dissociation reactions in the gas phase confirmed a very strong binding of pepstatin A by natively folded pepsin (N). ITEM-TWO further revealed the existence of two compactly folded in-solution pepsin conformers (C\n                    <jats:sup>a<\/jats:sup>\n                    and C\n                    <jats:sup>b<\/jats:sup>\n                    ) which also were able to bind pepstatin A. Binding strengths of the respective compactly folded pepsin conformer-containing complexes could be determined and apparent gas phase complex dissociation constants and reaction enthalpies differentiated these from each other and from the pepstatin A \u2013 pepsin complex which had been formed from natively folded pepsin. Thus, ITEM-TWO turned out to be well suited to pinpoint in-solution pepsin conformers by interrogating quantitative traits of pepstatin A \u2013 pepsin complexes in the gas phase.\n                  <\/jats:p>","DOI":"10.1177\/14690667231178999","type":"journal-article","created":{"date-parts":[[2023,6,1]],"date-time":"2023-06-01T02:34:05Z","timestamp":1685586845000},"page":"303-312","update-policy":"https:\/\/doi.org\/10.1177\/sage-journals-update-policy","source":"Crossref","is-referenced-by-count":2,"title":["Native and compactly folded\n                    <i>in-solution<\/i>\n                    conformers of pepsin are revealed and distinguished by mass spectrometric ITEM-TWO analyses of\n                    <i>gas-phase<\/i>\n                    pepstatin A \u2013 pepsin complex binding strength differences"],"prefix":"10.1177","volume":"29","author":[{"given":"Cornelia","family":"Koy","sequence":"first","affiliation":[{"name":"Proteome Center Rostock, Medical Faculty and Natural Science Faculty, University of Rostock, Rostock, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0004-5359-9528","authenticated-orcid":false,"given":"Ursula M","family":"Glocker","sequence":"additional","affiliation":[{"name":"Proteome Center Rostock, Medical Faculty and Natural Science Faculty, University of Rostock, Rostock, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Bright D","family":"Danquah","sequence":"additional","affiliation":[{"name":"Proteome Center Rostock, Medical Faculty and Natural Science Faculty, University of Rostock, Rostock, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9190-482X","authenticated-orcid":false,"given":"Michael O","family":"Glocker","sequence":"additional","affiliation":[{"name":"Proteome Center Rostock, Medical Faculty and Natural Science Faculty, University of Rostock, Rostock, 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