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Chloroplast function depends on the translocation of cytosolically synthesized precursor proteins into the organelle. The recognition and transfer of most precursor proteins across the outer membrane depend on a membrane inserted complex. Two receptor components of this complex, Toc34 and Toc159, are GTPases, which can be phosphorylated by kinases present in the hosting membrane. However, the physiological function of phosphorylation is not yet understood in detail. It is demonstrated that both receptors are phosphorylated within their G-domains. In vitro, the phosphorylation of Toc34 disrupts both homo- and heterodimerization of the G-domains as determined using a phospho-mimicking mutant. In endogenous membranes this mutation or phosphorylation of the wild-type receptor disturbs the association of Toc34, but not of Toc159 with the translocation pore. Therefore, phosphorylation serves as an inhibitor for the association of Toc34 with other components of the complex and phosphorylation can now be discussed as a mechanism to exchange different isoforms of Toc34 within this ensemble. [ABSTRACT FROM PUBLISHER]

Identifies the types of sorting signals in plant vacuoles used for protein transport. Structure of the conserved motif identified within the N-terminal propeptides; Binding action to a family of put ative sorting receptors for sequence-specific vacuolar sorting signals.

Examines the mechanisms in the endoplasmic reticulum (ER) of plants for retaining proteins. Properties of polypeptide retention in ER which are either signal-independent or dependent on specific retention signals encoded by the primary sequence of the polypeptide; Categories of synthesized polypeptides.

Describes the search for and identification of receptors for plant vascular protein and the characterization of their involvement in the protein secretory pathway to the vacuole. Presence of receptors in clathrin coated vesicles; Transport from the trans-Golgi network to the vacuole; SNAP receptors in vesicle fusion.