Fibril assembly and carotenoid overaccumulation in chromoplasts: a model for supramolecular lipoprotein structures.

Abstract

Chromoplast development in ripening bell pepper fruits is characterized by a massive synthesis of carotenoid pigments, resulting in their distinctlve red color. We have shown that 95% of these pigments accumulate in chromoplasts in speclfic lipoprotein fibrils. In addltion to carotenoids, purified fibrils contain galactolipids, phospholipids, and a single, 32-kD protein, designated fibrillin, which has antigenically related counterparts in other species. Fibrlls were reconstltuted in vitro when purified fibrillin was combined with carotenoids and polar llpids in the same stoichlometrlc ratlo found in fibrils in vivo. Antibodies dlrected against fibrillin were used to isolate a fibrillin cDNA clone and, in immunological studies, to follow its accumulation during the chloroplast-tothromoplast transltlon under different condltions. A model for fibril amhitecture is proposed wherein carotenoids accumulate in the center of the fibrils and are surrounded by a layer of polar lipids, which in turn are surrounded by an outer layer of fibrillin. Topological analysis of purlfied fibrils verified this structure. Collectively, these results suggest that the process of fibrll self-assembly in chromoplasts 1s an example of a general phenomenon shared among cells that target excess membrane llpids into deposit structures to avoid their destabilizing or toxic effects. In addition, we have shown that abscisic acid stimulates this phenomenon in chromoplasts, whereas gibberellic acid and auxin delay it.

Subfractionation of eyespot apparatuses from the green alga Spermatozopsis similis : isolation and characterization of eyespot globules

“…This, as well as the low total amounts of protein in the globule fraction, indicates that the globule-associated proteins are only minor components of the EA. This assumption also corresponds well with the general idea that carotenoid-rich bodies with a low protein:lipid ratio tend to form globular structures (Hansmann and Sitte 1982;Derue re et al 1994;Camara et al 1995). On the other hand, eyespot membranes exhibit a high intramembrane particle density (Melkonian and Robenek 1980a,b;.…”

“…The currently identi®ed globule-associated proteins are highly homologous to each other and their molecular masses are in the range of approx. 30±39 kDa (Derue re et al 1994;Vishnevetsky et al 1996;PozuetaRomero et al 1997;Kessler et al 1999). A homologue to ®brillin, one of these proteins, has also been detected in Synechocystis (Kaneko et al 1996).…”

“…In all of these structures, a central core of apolar substances (e.g. triacylglycerols, carotenoids) is surrounded by an electron-dense coat containing polar phospholipids and speci®c proteins (Hansmann and Sitte 1982;Knoth et al 1986;Derue re et al 1994;Huang 1996;Pozueta-Romero et al 1997;Kessler et al 1999). In addition to proteins involved in globule stabilization/interaction, further important proteins for assembly of the eyespot plate might be among the speci®cally enriched proteins, e.g.…”

Structure of a functional geranylgeranyl pyrophosphate synthase gene from Capsicum annuum

“…It is striking that the GGPPS gene is also uninterrupted since the available data suggest that this gene is coexpressed with the CCS gene during fruit ripening in C. annuum [ 3 ]. In contrast, the fibrillin gene appears to be induced earlier during fruit ripening and shows a different pattern of expression as judged by RNA gel blot analysis [6]. It is not known whether the presence ofintrons influences the expression of carotenoid biosynthetic genes.…”

Chlorophyll disappearance and chlorophyllase activity during ripening of Capsicum annuum L fruits

“…In chlorophyll-retaining cultivars, some thylakoids were preserved inside the microfibrillar network. 24,25 Decreasing chlorophyllase activity during ripening and senescence of the fruits may indicate that other enzymes were involved in the rapid disappearance of chlorophylls. Chlorophyllase activity and losses of chlorophyll were not correlated; Belrubi had high levels of both chlorophyllase activity and rate of chlorophyll disappearance, whereas the Delfin and NuMex cultivars had high rates of chlorophyll disappearance but low chlorophyllase activity.…”