Photosynthetic bacteria polypeptide subunits

Fig. 2. (A) SDS-PAGE electrophoresis showing the polypeptide subunits of the reaction-center of Rb. sphaeroides R-26 (B) and (C) SDS-PAGE electrophoresis patterns of the LM-complex and the H-subunit obtained by treating the reaction center with SDS/ LDAO followed by centrifugation in a sucrose-density gradient. Figure from Okamura, Steiner and Feher (1974) Characterization of reaction centers from photosynthetic bacteria. I. Subunit structure of the protein mediating the primary photochemistry in Rhodopseudomonas sphaeroides R-26. Biochemistry, 13 137, 138.

The basic structure of aU the component proteins making up the Light-harvesting (LH) complexes of purple photosynthetic bacteria is similar." " It consists of two polypeptides a- and jS-subunits) that fold into transmembrane Q -hehces and form a heterodimer that noncovalently binds bacteriochlorophyll... 

Photosynthetic bacteria such as Rhodopseudomonas viridis contain a photo-synthetic reaction center that has been revealed at atomic resolution. The bacterial reaction center consists of four polypeptides L (31 kd), M (36 kd), and H (28 kd) subunits and C, a c-type cytochrome with four c-type hemes (figure 19.9). Sequence comparisons and low-resolution structural studies have rmaled that the bacterial reaction center is homologous to the more complex plant systems. Thus, many of our observations of the bacterial system will apply to plant systems as well. 

Meadows KA, lida K, Tsuda K, Recchia PA, Heller BA, Antonio B, Nango M, and Loach PA. Enzymatic and Chemical Cleavage of the Core Light-Harvesting Polypeptides of Photosynthetic Bacteria - Determination of the Minimal Polypeptide Size and Structure Required for Subunit and Light-Harvesting Complex-Formation. Biochemistry 1995 34 1559-1574. 

Kehoe JW, Meadows KA, Parkes-Loach PS, and Loach PA. Reconstitution of core light-harvesting complexes of photosynthetic bacteria using chemically synthesized polypeptides. 2. Determination of structural features that stabilize complex formation and their implications for the structure of the subunit complex. Biochemistry 1998 37 3418-3428. 

Figure 23-28 (A) Model of a light-harvesting chlorosome from green photosynthetic sulfur bacteria such as Chlorobium tepidum and species of Prosthecochloris. The chlorosome is attached to the cytoplasmic membrane via a baseplate, which contains the additional antenna bacteriochlorophylls (795 BChl a) and is adjacent to the trimeric BChl protein shown in (B) and near the reaction center. After Li et al.302 and Remigy et a/.304 (B) Alpha carbon diagram of the polypeptide backbone and seven bound BChl a molecules in one subunit of the trimeric protein from the green photosynthetic bacterium Prosthecochloris. For clarity, the magnesium atoms, the chlorophyll ring substituents, and the phytyl chains, except for the first bond, are omitted. The direction of view is from the three-fold axis, which is horizontal, toward the exterior of the molecule. From Fenna and Matthews.305 See also Li et al.302...

---