Unusual characteristics of amino-terminal and hydrophobic domains in nuclear-encoded thylakoid signal peptides

被引:14
作者
Brink, S [1 ]
Bogsch, EG [1 ]
Mant, A [1 ]
Robinson, C [1 ]
机构
[1] UNIV WARWICK,DEPT BIOL SCI,COVENTRY CV4 7AL,W MIDLANDS,ENGLAND
来源
EUROPEAN JOURNAL OF BIOCHEMISTRY | 1997年 / 245卷 / 02期
关键词
chloroplast; protein transport; signal peptide; thylakoid;
D O I
10.1111/j.1432-1033.1997.00340.x
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
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.
引用
收藏
页码:340 / 348
页数:9
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