{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,4]],"date-time":"2026-10-04T17:20:34Z","timestamp":1791134434877,"version":"4.1.0"},"reference-count":37,"publisher":"National Academy of Sciences","issue":"5","content-domain":{"domain":["www.pnas.org"],"crossmark-restriction":true},"short-container-title":["Proc. Natl. Acad. Sci. U.S.A."],"published-print":{"date-parts":[[2007,1,30]]},"abstract":"<jats:p>Actin-related protein (Arp) 2\/3 complex nucleates new branches in actin filaments playing a key role in controlling eukaryotic cell motility. This process is tightly regulated by activating factors: ATP and WASp-family proteins. However, the mechanism of activation remains largely hypothetical. We used radiolytic protein footprinting with mass spectrometry in solution to probe the effects of nucleotide- and WASp-binding on Arp2\/3. These results represent two significant advances in such footprinting approaches. First, Arp2\/3 is the most complex macromolecular assembly yet examined; second, only a few picomoles of Arp2\/3 was required for individual experiments. In terms of structural biology of Arp 2\/3, we find that ATP binding induces conformational changes within Arp2\/3 complex in Arp3 (localized in peptide segments 5\u201318, 212\u2013225, and 318\u2013327) and Arp2 (within peptide segment 300\u2013316). These data are consistent with nucleotide docking within the nucleotide clefts of the actin-related proteins promoting closure of the cleft of the Arp3 subunit. However, ATP binding does not induce conformational changes in the other Arp subunits. Arp2\/3 complex binds to WASp within the C subdomain at residue Met 474 and within the A subdomain to Trp 500. Our data suggest a bivalent attachment of WASp to Arp3 (within peptides 162\u2013191 and 318\u2013329) and Arp2 (within peptides 66\u201380 and 87\u201397). WASp-dependent protections from oxidation within peptides 54\u201365 and 80\u201391 of Arp3 and in peptides 300\u2013316 of Arp2 suggest domain rearrangements of Arp2 and Arp3 resulting in a closed conformational state consistent with an \u201cactin-dimer\u201d model for the active state.<\/jats:p>","DOI":"10.1073\/pnas.0605380104","type":"journal-article","created":{"date-parts":[[2007,1,25]],"date-time":"2007-01-25T00:50:27Z","timestamp":1169686227000},"page":"1552-1557","update-policy":"https:\/\/doi.org\/10.1073\/pnas.cm10313","source":"Crossref","is-referenced-by-count":58,"title":["Visualizing Arp2\/3 complex activation mediated by binding of ATP and WASp using structural mass spectrometry"],"prefix":"10.1073","volume":"104","author":[{"given":"Janna G.","family":"Kiselar","sequence":"first","affiliation":[{"name":"*Case Center for Proteomics 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