Anja Schneider - Manganese Transporter in Chloroplasts
- Datum: 30.10.2019
- Uhrzeit: 14:00 - 15:30
- Vortragende(r): Anja Schneider
- Ort: Central Building
- Raum: Seminar Room
- Gastgeber: Ute Armbruster
Plants, like all other
living organism, require manganese (Mn) as an activator of enzymes or as an
integral component of protein complexes. The most prominent role of Mn is its
involvement in the oxygen evolving complex of photosystem II (PSII), which
splits water into oxygen, protons and electrons. The electrons released from
water in PSII are eventually transferred to NADP+ via the cytochrome b6/f
complex, plastocyanin, photosystem I, and ferredoxin. To reach its destination
in the oxygen-evolving complex of PSII in the thylakoid lumen, Mn must cross
all three chloroplast membranes (the outer and inner envelopes and the
thylakoid membrane). The outer envelope membrane is non-selectively permeable
to most ions, while the inner envelope and the thylakoid membrane possess
specific transport proteins. At the inner envelope membrane, the CHLOROPLAST
MANGANESE TRANSPORTER1 (CMT1) represents the first candidate for the
long-sought Mn import protein that transports Mn from the cytosol into the
chloroplast stroma. The Arabidopsis mutant cmt1 exhibits severe
growth retardation, disruption of chloroplast ultrastructure and reduction of
PSII activity, in association with a significant drop in the level of Mn in the
organelle. The protein responsible for the transport of Mn from the chloroplast
stroma into the thylakoid lumen is PHOTOSYNTHESIS AFFECTED MUTANT71 (PAM71).
PAM71 resides in the thylakoid membrane und in pam71 mutants PSII
function is specifically impaired at the oxygen-evolving complex. The Mn
transport function of CMT1 and PAM71 is conserved among homologous proteins from
other oxygenic photosynthetic organisms, e.g. cyanobacteria and green algae and
a homologous protein is also found in human. Mn deficiency of pam71 can
be rescued if the human protein is targeted to the thylakoid membrane in this
mutant, indicating a similar transport function.