Hydrogen/deuterium exchange and aggregation of a polyvaline and a polyleucine α-helix investigated by matrix-assisted laser desorption ionization mass spectrometry

被引:29
作者
Hosia, W [1 ]
Johansson, J [1 ]
Griffiths, WJ [1 ]
机构
[1] Karolinska Inst, Dept Med Biochem & Biophys, S-17177 Stockholm, Sweden
关键词
D O I
10.1074/mcp.M200042-MCP200
中图分类号
Q5 [生物化学];
学科分类号
071010 ; 081704 ;
摘要
The membrane-associated pulmonary surfactant protein C (SP-C), containing a polyvaline a-helix, and a synthetic SP-C analogue with a polyleucine helix (SP-C(Leu)) were studied by hydrogen/deuterium exchange matrix-assisted laser desorption ionization (MALDI) mass spectrometry. SP-C, but not SP-C(Leu), formed abundant amyloid fibrils under experimental conditions. In CD3OD/D2O, 91:9 (v/v) containing 2 mm ammonium acetate, SP-C(Leu) and SP-C exchanged 40% of their exchangeable hydrogens within 1 min. This corresponds to exchange of labile side-chain hydrogen atoms, hydrogens on the N- and C-terminal heteroatoms, and amide hydrogen atoms in the unstructured N-terminal regions. After similar to300 h, four exchangeable hydrogen atoms in SP-C(Leu) and 10 in SP-C remained unexchanged. During this time period the ion current corresponding to singly charged SP-C decreased to < 10% of the initial value due to the formation of insoluble aggregates that are not detected by MALDI mass spectrometry. In contrast, the ion current for SP-C(Leu) was maintained over this time period, although the peptides were incubated together. In combination, hydrogen/deuterium exchange and aggregation data indicate that the polyleucine peptide refolds into a helix after opening, while the unfolded polyvaline peptide forms insoluble beta-sheet aggregates rather than refolding into a helix. The SP-C helix, but not the SP-C(Leu) helix, is thus in a metastable state, which may contribute to the recently observed tendency of SP-C and its precursor to misfold and aggregate in vivo.
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页码:592 / 597
页数:6
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