Relationship of Chlorophyll Biosynthesis to the Assembly of Chlorophyll-Protein Complexes - Chlorophyll Biosynthesis and Technological Applications - page 320

Fig. 15.1 Schematics of the SBP-single location model in a PSU. As an example, the functional-
ity of the model was illustrated with the use of three apoproteins namely CP29, LCHI-730 and
CP47. Abbreviations: SBP single-branched Chl biosynthetic pathway, PSII photosystem II,
LHCII, the major light-harvesting Chl-protein complex of PSII, LHCI, one of the LHC antennae
of PSI, CP47 and CP29, two PSII antennae, LHCI-730, the LHC antenna of PSI. Curved lines
indicate putative energy transfer between tetrapyrroles and a Chl-protein complex (Adapted from
Rebeiz et al. 2003b )
subcenter, distances separating metabolic tetrapyrroles from the Chl-protein
complexes are shorter than in the SBP-single-location model.
15.2.1.3 Multibranched-Pathway (MBP)-Sublocation Model
In the MBP-sublocation model (Fig. 15.4 ), the unified multi-branched Chl a/b
biosynthetic pathway is visualized as the template of a Chl-protein biosynthesis
center where the assembly of PSI, PSII and LHC take place (Kolossov et al. 2003 ;
Rebeiz et al. 2003b ). The multiple Chl biosynthetic routes are visualized, individu-
ally or in groups of one or several adjacent routes, as Chl-apoprotein thylakoid
biosynthesis subcenters earmarked for the coordinated assembly of individual
Chl-apoprotein complexes. Apoproteins destined to some of the biosynthesis
subcenters may possess specific signals for specific Chl biosynthetic enzymes
peculiar to that subcenter, such as 4-vinyl reductases, formyl synthetases or Chl
a and Chl b synthetases. Once an apoprotein, formed in the cytoplasm or in the
plastid, reaches its biosynthesis subcenter destination and its signal is split off, it
binds nascent Chl formed via one or more biosynthetic routes. During Chl binding,
the apoprotein folds properly and act at that location, while folding or after folding,
as a template for the assembly of other apoproteins. In this case too, shorter
distances separate the accumulated tetrapyrroles from the Chl-protein complexes.