UNSPECIFIED (1996) Ricin A chain fused to a chloroplast-targeting signal is unfolded on the chloroplast surface prior to import across the envelope membranes. JOURNAL OF BIOLOGICAL CHEMISTRY, 271 (8). pp. 4082-4085. ISSN 0021-9258

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Abstract

The initial stages of chloroplast protein import involve the binding of precursor proteins to surface-bound receptors prior to translocation across the envelope membranes in a partially folded conformation, We have analyzed the unfolding process by examining the conformation of a construct, comprising the presequence of a chloroplast protein linked to ricin A chain, before and after binding to the chloroplast surface, We show that the presequence is highly susceptible to proteolysis in solution, probably reflecting a lack of tertiary structure, whereas the A chain passenger protein is resistant to extremely high concentrations of protease, unless deliberately unfolded using denaturant, The A chain moiety is furthermore active, indicating that the presence of the presequence does not prevent formation of a tightly folded, native state, In contrast, receptor-bound p33KRA (fusion protein comprising the 33-kDa presequence plus 22 residues of mature protein, linked to the A chain of ricin) is quantitatively digested by protease concentrations that have little effect on the A chain in solution, We conclude that protein unfolding can take place on the chloroplast surface in the absence of translocation and without the aid of soluble factors.

Item Type:	Journal Article
Subjects:	Q Science > QD Chemistry
Journal or Publication Title:	JOURNAL OF BIOLOGICAL CHEMISTRY
Publisher:	AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
ISSN:	0021-9258
Date:	23 February 1996
Volume:	271
Number:	8
Number of Pages:	4
Page Range:	pp. 4082-4085
Publication Status:	Published
URI:	http://wrap.warwick.ac.uk/id/eprint/19051

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