Structural Reorganization of Proteins Revealed by Radiolysis and Mass Spectrometry: G-Actin Solution Structure Is Divalent Cation Dependent

详细信息    查看全文

• 作者：Jing-Qu Guan ; Steven C. Almo ; Emil Reisler ; and Mark R. Chance
• 刊名：Biochemistry
• 出版年：2003
• 出版时间：October 21, 2003
• 年：2003
• 卷：42
• 期：41
• 页码：11992 - 12000
• 全文大小：259K
• 年卷期：v.42,no.41(October 21, 2003)
• ISSN：1520-4995

文摘

The solution structures of isolated monomeric actins in their Mg²⁺-ATP and Ca²⁺-ATP boundforms and in complexes with gelsolin segment-1 have been probed using hydroxyl radicals (·OH) generatedby synchrotron X-ray radiolysis. Proteolysis and mass spectrometry analysis of 28 peptides containing 58distinct reactive probe sites within actin were used to monitor conformational variations linked to divalentcation and gelsolin segment-1 binding. The solvent accessibilities of the probe sites, as measured byfootprinting in solution for the Ca²⁺-G-actin and Mg²⁺-G-actin complexes with gelsolin segment-1, wereconsistent with available crystallographic data. This included a specific protection at the contact interfacebetween the partners, as revealed by reduced reactivity of peptide 337-359 in the complex. Aside fromthe specific protection indicated previously, the oxidation rates for the reactive residues of the isolatedCa²⁺-G-actin were similar to those of the actin gelsolin segment-1 complexes; however, the reactivity ofnumerous residues in the isolated Mg²⁺-G-actin form was significantly reduced. Specifically, Mg²⁺-G-actin has a set of protected sites relative to Ca²⁺-G-actin that suggest a structural reorganization insubdomains 4 and 2 and a C-terminus more closely packed onto subdomain 1. These conformationalvariations for isolated Mg²⁺-G-actin provide a structural basis for its greater tendency to polymerize intofilaments as compared to Ca²⁺-G-actin.