Chlorophyll exchange on reconstituted LHCII: Chlorophyll a is essential for Trimerisation

Mutant Trimers of Light-Harvesting Complex II Exhibit Altered Pigment Content and Spectroscopic Features

“…Later, it was found that the Chl a :Chl b ratio of LHC-II from Chlorella fusca can change upon addition of Chl a or b to isolated thylakoids (). It has been shown that under certain conditions LHC-II monomers can fold in vitro with only Chl b and carotenoids present, although the same does not hold for Chl a ( , ). Recently, a detailed spectroscopic investigation was performed on complexes with low Chl a :Chl b ratios ().…”

Pigment Assembly—Transport and Ligation

“…Chl a4 is neighboring a5 and could indirectly destabilize the trimer by destabilizing Chl a5. It may be interesting in this context that, as mentioned above (Section V.A), LHCIIb monomers can be reconstituted in vitro with Chl b as the only Chl, however for trimer formation, at least one Chl a per trimer is needed (Rogl et al, 1998;Kleima et al, 1999). It is therefore tempting to speculate that this would be a Chl a near the center of the trimeric complex like one in a Chl a5 position.…”

“…However, if reconstitution and subsequent complex isolation is performed under milder conditions (e.g. with a less strongly denaturing detergent at a lower temperature), the Chl a/b ration in the recombinant complexes can vary within rather wide limits (Rogl et al, 1998, Kleima et al, 1999. Furthermore, a monomeric LHCIIb complex can be formed in the absence of Chl a; however, no stable pigment-protein complex is obtained in the absence of Chl b (Rogl et al, 1998).…”

“…with a less strongly denaturing detergent at a lower temperature), the Chl a/b ration in the recombinant complexes can vary within rather wide limits (Rogl et al, 1998, Kleima et al, 1999. Furthermore, a monomeric LHCIIb complex can be formed in the absence of Chl a; however, no stable pigment-protein complex is obtained in the absence of Chl b (Rogl et al, 1998). It should be noted however that the recombinant LHCIIb versions significantly deviating from the native Chl a/b ratio are considerably less stable than the native complex or recombinant complexes reconstituted to obtain a Chl a/b ratio of about 1.1.…”

“…The most likely explanation is that Chl binding into non-specific binding sites results in a significant loss of stability for the complex in the thylakoid membrane. In the case of LHCIIb, the selection for properly pigmented proteins possibly occurs on the level of trimeric complexes, as trimer formation in vitro seems to be more critical with respect to the proper Chl a/b ratio than the reconstitution of monomers (Rogl et al, 1998;Kleima et al, 1999).…”