Conformation of a purified "spontaneously" inserting thylakoid membrane protein precursor in aqueous solvent and detergent micelles
UNSPECIFIED. (2001) Conformation of a purified "spontaneously" inserting thylakoid membrane protein precursor in aqueous solvent and detergent micelles. JOURNAL OF BIOLOGICAL CHEMISTRY, 276 (18). pp. 14607-14613. ISSN 0021-9258Full text not available from this repository.
Subunit W of photosystem II (PsbW) is a single-span thylakoid membrane protein that is synthesized with a cleavable hydrophobic signal peptide and integrated into the thylakoid membrane by an apparently spontaneous mechanism. In this study, we have analyzed the secondary structure of the pre-protein at early stages of the insertion pathway, using purified recombinant pre-PsbW. We show that the protein remains soluble in Tris buffer after removal of detergent. Under these conditions pre-PsbW contains no detectable alpha -helix, whereas substantial alpha -helical. structure is present in SDS micelles, In aqueous buffer, the tryptophan fluorescence emission characteristics are intermediate between those of solvent exposed and hydrophobic environments, suggesting the formation of a partially folded structure. If denaturants are excluded from the purification protocol, pre-PsbW purifies instead as a 180-kDa oligomer with substantial alpha -helical structure. Mature-size PsbW was prepared by removal of the presequence, and we show that this protein also contains alpha -helix in detergent but in lower quantities than the pre-protein. We therefore propose that pre-PsbW contains alpha -helical structure in both the mature protein and the signal peptide in nonpolar environments. We propose that pre-PsbW acquires its alpha -helical structure only during the later, membrane-bound stages of the insertion pathway, after which it forms a "helical hairpin"-type loop intermediate in the thylakoid membrane.
|Item Type:||Journal Article|
|Subjects:||Q Science > QD Chemistry|
|Journal or Publication Title:||JOURNAL OF BIOLOGICAL CHEMISTRY|
|Publisher:||AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC|
|Date:||4 May 2001|
|Number of Pages:||7|
|Page Range:||pp. 14607-14613|
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