Thylakoids are a formation of flattened membrane vesicles and protein complexes found in cyanobacteria, algae and plants. In the chloroplasts of land plants the thylakoid membrane systems form a network of densely packed stacks called grana lamellae, which are connected by unstacked stroma lamellae. Photosystem II is mainly localized in the appressed grana region, while photosystem I and the ATP synthase complexes are enriched in the stroma lamellae. The cytochrome b₆/f complex is distributed laterally throughout both stacked and unstacked membrane regions. The photosynthetic complexes consist of integral and peripheral proteins. The first part of this protocol (A) shows how to fractionate thylakoids into grana and stroma lamellae. The second part of this protocol (B) shows how to distinguish between strong hydrophobic integral membrane associations and weak electrostatic membrane and/or membrane complex associations. As it is necessary to specifically detect the protein of interest in the fractions, a specific antibody raised against the protein of interest or a complemented null mutant of a structural component expressing a tagged fusion protein would be of great advantage. The last part of this protocol (C) shows, how to investigate the topology of integral and peripheral proteins. This method requires a specific antibody for the protein of interest. For integral membrane proteins peptide-specific antibodies or epitope-tagged versions are required. The protocol is suitable for the investigation of low molecular weight proteins (LMW) below 5 kDa (Torabi et al., 2014).

Stroma (基质)

Grana (基粒)

Photosystem (光系统)

Topology (拓扑)

Thylakoid (类囊体)