Figure 9.

Working model for the assembly and function of the OHP1-OHP2-HCF244 heterotrimeric complex. A, The formation of the heterotrimer begins with the association of HCF244 to OHP2. The N-terminal end of OHP2 is facing the stroma and involved in binding HCF244. This dimer already possesses partial activity, and dimer formation is required for the subsequent binding of OHP1. The heterotrimeric complex is formed when OHP1 associates with OHP2 in the membrane and, furthermore, with the membrane-associated HCF244. HCF244 is required to stably hold OHP1 in the trimeric complex. B, In our model, the OHP heterodimer is involved in the delivery of chlorophylls to newly synthesized D1 proteins, whereas HCF244 is involved in the translation initiation of psbA. A stable interaction or complex formation of either OHPs or HCF244 with CHLG is unlikely (indicated by red arrows), although a transient and/or weak interaction cannot be excluded.