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Three broad applications illustrate that the features present in weak electron density can reveal important, unanticipated conformational heterogeneity in proteins. The methods introduced here help convert X-ray crystallography from the principal technique to obtain \u201csnapshots\u201d of biological molecules to an approach that also can reveal the signatures of molecular motions that are potentially important for function. These advances have broad implications for developing drugs and understanding protein mechanisms.<\/jats:p>","DOI":"10.1073\/pnas.1302823110","type":"journal-article","created":{"date-parts":[[2013,12,21]],"date-time":"2013-12-21T01:33:33Z","timestamp":1387589613000},"page":"237-242","update-policy":"https:\/\/doi.org\/10.1073\/pnas.cm10313","source":"Crossref","is-referenced-by-count":100,"title":["Protein structural ensembles are revealed by redefining X-ray electron density noise"],"prefix":"10.1073","volume":"111","author":[{"given":"P. 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