{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,1]],"date-time":"2026-10-01T22:05:44Z","timestamp":1790892344676,"version":"4.1.0"},"reference-count":55,"publisher":"Wiley","issue":"5","license":[{"start":{"date-parts":[[2009,2,23]],"date-time":"2009-02-23T00:00:00Z","timestamp":1235347200000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Protein Science"],"published-print":{"date-parts":[[2009,5]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:p>A disulfide\u2010linked nitroxide side chain (R1) used in site\u2010directed spin labeling of proteins often exhibits an EPR spectrum characteristic of a weakly ordered z\u2010axis anisotropic motion at topographically diverse surface sites, including those on helices, loops and edge strands of \u03b2\u2010sheets. To elucidate the origin of this motion, the first crystal structures of R1 that display simple z\u2010axis anisotropic motion at solvent\u2010exposed helical sites (131 and 151) and a loop site (82) in T4 lysozyme have been determined. Structures of 131R1 and 151R1 determined at cryogenic or ambient temperature reveal an intraresidue C<jats:sub>\u03b1<\/jats:sub>\uf8ffH\u00b7\u00b7\u00b7S<jats:sub>\u03b4<\/jats:sub> interaction that immobilizes the disulfide group, consistent with a model in which the internal motions of R1 are dominated by rotations about the two terminal bonds (Columbus, K\u00e1lai, Jeko, Hideg, and Hubbell, Biochemistry 2001;40:3828\u20133846). Remarkably, the 131R1 side chain populates two rotamers equally, but the EPR spectrum reflects a single dominant dynamic population, showing that the two rotamers have similar internal motion determined by the common disulfide\u2010backbone interaction. The anisotropic motion for loop residue 82R1 is also accounted for by a common disulfide\u2010backbone interaction, showing that the interaction does not require a specific secondary structure. If the above observations prove to be general, then significant variations in order and rate for R1 at noninteracting solvent\u2010exposed helical and loop sites can be assigned to backbone motion because the internal motion is essentially constant.<\/jats:p>","DOI":"10.1002\/pro.96","type":"journal-article","created":{"date-parts":[[2009,2,23]],"date-time":"2009-02-23T22:21:32Z","timestamp":1235427692000},"page":"893-908","source":"Crossref","is-referenced-by-count":107,"title":["Structural origin of weakly ordered nitroxide motion in spin\u2010labeled proteins"],"prefix":"10.1002","volume":"18","author":[{"given":"Mark R.","family":"Fleissner","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Duilio","family":"Cascio","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Wayne L.","family":"Hubbell","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2009,4,21]]},"reference":[{"key":"e_1_2_6_2_2","first-page":"251","volume-title":"Spin labeling: The next millennium","author":"Feix JB","year":"1998"},{"key":"e_1_2_6_3_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0959-440X(98)80158-9"},{"key":"e_1_2_6_4_2","doi-asserted-by":"publisher","DOI":"10.1038\/78956"},{"key":"e_1_2_6_5_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0968-0004(02)02095-9"},{"key":"e_1_2_6_6_2","doi-asserted-by":"publisher","DOI":"10.1021\/bi011856z"},{"key":"e_1_2_6_7_2","doi-asserted-by":"publisher","DOI":"10.1016\/j.sbi.2006.08.008"},{"key":"e_1_2_6_8_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0079-6603(08)00005-6"},{"key":"e_1_2_6_9_2","doi-asserted-by":"publisher","DOI":"10.1073\/pnas.0600733103"},{"key":"e_1_2_6_10_2","doi-asserted-by":"publisher","DOI":"10.1038\/nsmb1129"},{"key":"e_1_2_6_11_2","doi-asserted-by":"publisher","DOI":"10.1073\/pnas.0607972103"},{"key":"e_1_2_6_12_2","doi-asserted-by":"publisher","DOI":"10.1073\/pnas.0708258104"},{"key":"e_1_2_6_13_2","doi-asserted-by":"publisher","DOI":"10.1073\/pnas.0802515105"},{"key":"e_1_2_6_14_2","doi-asserted-by":"publisher","DOI":"10.1006\/jmra.1996.0113"},{"key":"e_1_2_6_15_2","doi-asserted-by":"publisher","DOI":"10.1021\/bi960482k"},{"key":"e_1_2_6_16_2","doi-asserted-by":"publisher","DOI":"10.1021\/bi0360962"},{"key":"e_1_2_6_17_2","doi-asserted-by":"publisher","DOI":"10.1021\/bi000604f"},{"key":"e_1_2_6_18_2","doi-asserted-by":"publisher","DOI":"10.1110\/ps.062739107"},{"key":"e_1_2_6_19_2","doi-asserted-by":"publisher","DOI":"10.1110\/ps.073174008"},{"key":"e_1_2_6_20_2","doi-asserted-by":"publisher","DOI":"10.1021\/bi0497906"},{"key":"e_1_2_6_21_2","doi-asserted-by":"publisher","DOI":"10.1021\/bi002645h"},{"key":"e_1_2_6_22_2","doi-asserted-by":"publisher","DOI":"10.1021\/bi9826310"},{"key":"e_1_2_6_23_2","doi-asserted-by":"publisher","DOI":"10.1021\/jp0629487"},{"key":"e_1_2_6_24_2","doi-asserted-by":"publisher","DOI":"10.1038\/sj.emboj.7601614"},{"key":"e_1_2_6_25_2","doi-asserted-by":"publisher","DOI":"10.1021\/bi00105a002"},{"key":"e_1_2_6_26_2","doi-asserted-by":"publisher","DOI":"10.1002\/1097-0134(20000815)40:3<389::AID-PROT50>3.0.CO;2-2"},{"key":"e_1_2_6_27_2","doi-asserted-by":"publisher","DOI":"10.1006\/jmbi.2001.4891"},{"key":"e_1_2_6_28_2","unstructured":"SezerD(2008)Molecular dynamics and ESR spectra of a nitroxide spin label at solvent\u2010exposed surfaces in proteins. 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