Mechanism and phylogeny of thylakoidal protein transport
Klösgen, R.B., Karnauchov, I., Berghöfer, J.
Botanisches Institut der LMU, Menzinger Straße 67, D-80638 München, Germany
Protein transport across the thylakoid membrane of higher plant chloroplasts proceeds via at least four different pathways that are protein-specific and mechanistically distinct (reviewed in [1]). Prokaryotic origin is undisputed only for the Sec- and SRP- pathways, since mechanistically similar protein transport routes exist in E. coli. Also spontaneous membrane integration like that described for CFo-II [2]. finds an equivalent in prokaryotes, notably in the membrane insertion of M13 procoat. However, neither the prokaryotic homologs of CFo-II nor its plastome encoded sister protein CFo-I seem to utilize this mechanism for integration which implies an unusual phylogeny of this pathway. The phylogenetic origin of the thylakoidal delta pH-dependent pathway is particularly ambigous. Until recently, it was widely considered to be a new development of the chloroplast, because a comparable transport mechanism had not been described elsewhere and the proteins targeted by this pathway were not found in cyanobacteria. However, data of an ancient component of the thylakoid membrane will be presented which is found in both chloroplasts and cyanobacteria and is targeted by the delta pH-pathway. This suggests that a similar pathway might exist also in prokaryotes. In contrast to the "typical" delta pH-mechanism, membrane transport in this case involves stromal component(s). Furthermore, the targeting signal differs significantly from that of other delta pH-type transport signals. These data suggest that the protein might represent a missing link in the development of the delta pH-dependent transport route.
Supported by the Deutsche Forschungsgemeinschaft (SFB 184)
[1] Klösgen (1997) J. Photochem. Photobiol. B: Biology 38, 1-9
[2] Michl et al., (1994) EMBO J. 13, 1310-1317
| LOCATION |
DATE |
TIME |
| Lecture Hall I |
Monday, April 6 |
04:50 pm |