UNSPECIFIED (1997) Unusual characteristics of amino-terminal and hydrophobic domains in nuclear-encoded thylakoid signal peptides. EUROPEAN JOURNAL OF BIOCHEMISTRY, 245 (2). pp. 340-348. ISSN 0014-2956

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Abstract

Thylakoid transfer signals carry information specifying translocation by either a Sec- or Delta pH-dependent protein translocator in the chloroplast thylakoid membrane, yet ail resemble classical signal peptides in overall structural terms. Comparison of known transfer signals reveals two differences: (a) signals for the Delta pH-driven system invariably contain a critical twin-arginine (Arg-Arg) motif prior to the hydrophobic (H) domain, whereas known Sec-dependent signals contain lysine, and (b) the H-domains of Sec-dependent signals are generally longer. Previous work has shown that a twin-Arg motif before the H-domain is critical for targeting by the Delta pH-dependent pathway; in this report we shaw that the charge characteristics of this region are not important for sorting by the Sec pathway. Twin-Lys, twin-Arg or single Arg are all acceptable to the Sec system, although single Lys/Arg is preferred. The single Lys in pre-plastocyanin can even be replaced by an uncharged residue without apparent effect. We have also generated a pre-plastocyanin mutant containing an H-domain which, in terms of hydropathy profile, is identical to that of a Delta pH-dependent protein. This mutant is also transported efficiently by the Sec system, demonstrating that hydrophobicity per se is not a key sorting determinant. However, the characteristics of the H-domain may be important in avoiding a different form of mis-targeting: to the endoplasmic reticulum. Thylakoid signal peptides have undergone substantial structural changes during the evolution of the chloroplast from endosymbiotic cyanobacterium: plastid-encoded and cyanobacterial signals contain H-domains that are highly hydrophobic and enriched in Leu and aromatic residues, whereas nuclear-encoded counterparts are Ala-rich and far less hydrophobic. We speculate that this trend may reflect a need to avoid mistargeting through recognition by cytosolic signal recognition particle, which preferentially interacts with more hydrophobic signal peptides.

Item Type:	Journal Article
Subjects:	Q Science > QD Chemistry
Journal or Publication Title:	EUROPEAN JOURNAL OF BIOCHEMISTRY
Publisher:	SPRINGER VERLAG
ISSN:	0014-2956
Date:	15 April 1997
Volume:	245
Number:	2
Number of Pages:	9
Page Range:	pp. 340-348
Publication Status:	Published
URI:	http://wrap.warwick.ac.uk/id/eprint/17852

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