TY - JOUR
T1 - The precursor of PsaD assembles into the photosystem I complex in two steps
AU - Minai, Limor
AU - Cohen, Yuval
AU - Chitnis, Parag R.
AU - Nechushtai, Rachel
PY - 1996/6/25
Y1 - 1996/6/25
N2 - The present study addresses the assembly in the chloroplast thylakoid membranes of PsaD, a peripheral membrane protein of the photosystem I complex. Located on the stromal side of the thylakoids, PsaD was found to assemble in vitro into the membranes in its precursor (pre-PsaD) and also in its mature (PsaD) form. Newly assembled unprocessed pre-PsaD was resistant to NaBr and alkaline wash. Yet it was sensitive to proteolytic digestion. In contradistinction, when the assembled precursor was processed, the resulting mature PsaD was resistant to proteases to the same extent endogeneous PsaD. The accumulation of protease-resistant PsaD in the thylakoids correlated with the increase of mature-PsaD in the membranes. This protection of mature PsaD from proteolysis could not be observed when PsaD was in a soluble form-i.e. not assembled within the thylakoids. The data suggest that pre-PsaD assembles to the membranes and only in a second step processing takes place. The observation that the assembly of pre-PsaD is affected by salts to a much lesser extent than that of mature-PsaD supports a two-step assembly of pre- PsaD.
AB - The present study addresses the assembly in the chloroplast thylakoid membranes of PsaD, a peripheral membrane protein of the photosystem I complex. Located on the stromal side of the thylakoids, PsaD was found to assemble in vitro into the membranes in its precursor (pre-PsaD) and also in its mature (PsaD) form. Newly assembled unprocessed pre-PsaD was resistant to NaBr and alkaline wash. Yet it was sensitive to proteolytic digestion. In contradistinction, when the assembled precursor was processed, the resulting mature PsaD was resistant to proteases to the same extent endogeneous PsaD. The accumulation of protease-resistant PsaD in the thylakoids correlated with the increase of mature-PsaD in the membranes. This protection of mature PsaD from proteolysis could not be observed when PsaD was in a soluble form-i.e. not assembled within the thylakoids. The data suggest that pre-PsaD assembles to the membranes and only in a second step processing takes place. The observation that the assembly of pre-PsaD is affected by salts to a much lesser extent than that of mature-PsaD supports a two-step assembly of pre- PsaD.
KW - peripheral membrane proteins
KW - protein folding
KW - thylakoids
UR - http://www.scopus.com/inward/record.url?scp=0029902024&partnerID=8YFLogxK
U2 - 10.1073/pnas.93.13.6338
DO - 10.1073/pnas.93.13.6338
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C2 - 8692816
AN - SCOPUS:0029902024
SN - 0027-8424
VL - 93
SP - 6338
EP - 6342
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 13
ER -