Complex Formation of Vipp1 Depends on Its α-Helical PspA-like Domain

Abstract

Vipp1 (vesicle-inducing protein in plastids 1) is found in Cyanobacteria and chloroplasts of photosynthetic eukaryotes where it is essential for the formation of the thylakoid membrane. Vipp1 is closely related to the phage shock protein A (PspA), a bacterial protein induced under diverse stress conditions. Vipp1 proteins differ from PspA by an additional C-terminal domain that is required for Vipp1 function in thylakoid biogenesis. We show here that in Cyanobacteria, green algae, and vascular plants, Vipp1 is part of a high molecular mass complex. The complex is formed by multiple copies of Vipp1, and complex formation involves interaction of the central ␣-helical domain that is common to Vipp1 as well as to PspA proteins. In chloroplasts of vascular plants, the Vipp1 complex can be visualized by green fluorescent protein fusion in discrete locations at the inner envelope. Green fluorescent protein fusion analysis furthermore revealed that complex formation is important for proper positioning of Vipp1 at the inner envelope of chloroplasts.Oxygenic photosynthesis is a specific feature of Cyanobacteria and chloroplasts of plants and algae. Characteristic of oxygenic photosynthesis is a specialized membrane system, the thylakoids, on which the components of the photosynthetic machinery are located (1). Despite its importance in the process of oxygenic photosynthesis, very little is known about the origin of the thylakoid membrane system in the ancestry of present day Cyanobacteria. Furthermore, proteins and other factors that are involved in the formation and maintenance of the thylakoid membrane in either Cyanobacteria or chloroplasts are not well defined.We have shown recently that in Arabidopsis as well as in Synechocystis the Vipp1 1 protein is essential for thylakoid biogenesis (2, 3). ⌬-vipp1 mutants, in which the expression of the vipp1 gene is greatly reduced, have lost their ability to build up a thylakoid membrane system and to perform oxygenic photosynthesis (2, 3). Interestingly, disruption of the vipp1 gene in Arabidopsis also abolished chloroplast vesicle transport, which has an alleged function in thylakoid formation in the chloroplasts of higher plants (2, 4). Vipp1 is closely related to PspA, a bacterial protein that is induced under distinct stress conditions, i.e. invasion by filamentous phages, inhibition of lipid biosynthesis, secretion defects, or the saturation of the twin arginine pathway (5-8). PspA and Vipp1 are distinguished by a C-terminal domain of about 20 -30 amino acids which is present in all Vipp1 proteins but lacking in PspA (3). It is presumed that this C-terminal extension is important for the role of Vipp1 in thylakoid biogenesis. Most Cyanobacteria possess genes coding for both PspA and Vipp1. Chloroplasts seem to have retained solely Vipp1, indicating that the function of PspA is no longer required in this organelle.So far, the exact function of PspA and Vipp1 remains elusive. In bacteria, PspA is part of a larger operon encoding four more proteins, PspB-PspE. PspA is induce...

Glycerolipid transfer for the building of membranes in plant cells

“…In vipp1 (a VIPP -Vesicle Inducing Protein in Plastid 1-deleted mutant), thylakoid membrane formation and chloroplast vesicle transport are abolished, indicating that VIPP1 is essential for thylakoid maintenance by a vesicular pathway. Recent data demonstrate that VIPP1 organizes in a high molecular mass complex closely associated with the inner envelope membrane and suggest that the C-terminus of the protein protrudes from the complex into the stroma of chloroplasts possibly for interaction with some other proteins [77]. Accordingly, soluble VIPP1 interacts with a HSP70B/CDJ2 chaperone pair [78].…”

Organization into Higher Ordered Ring Structures Counteracts Membrane Binding of IM30, a Protein Associated with Inner Membranes in Chloroplasts and Cyanobacteria

“…Although the tertiary structure of IM30 is not yet resolved, it is clear that IM30 monomers interact and assemble into large oligomeric ring complexes with molecular masses exceeding 2 MDa (5,14). However, from a common building block, not a single ring species is formed, rather IM30 forms various ring structures with different rotational symmetries (5, 14 -16).…”

“…Based on computational analyses, IM30 contains seven ␣-helices, which are interrupted by small random coil domains, and these ␣-helices are predicted to be involved in the formation of coiled-coil structures (5,6,14,15). Although the tertiary structure of IM30 is not yet resolved, it is clear that IM30 monomers interact and assemble into large oligomeric ring complexes with molecular masses exceeding 2 MDa (5, 14).…”

“…IM30 does not exhibit membrane spanning helices, as is typical for a canonical transmembrane protein (2, 3), and thus, it appears to peripherally bind to the cytoplasmic surface of the inner envelope/cytoplasmic membrane and TMs (5, 13). In fact, IM30 appears to exist in equilibrium between a soluble and a membrane-attached form (5).Based on computational analyses, IM30 contains seven ␣-helices, which are interrupted by small random coil domains, and these ␣-helices are predicted to be involved in the formation of coiled-coil structures (5,6,14,15). Although the tertiary structure of IM30 is not yet resolved, it is clear that IM30 monomers interact and assemble into large oligomeric ring complexes with molecular masses exceeding 2 MDa (5, 14).…”

Subcellular localization and functions of the barley stem rust resistance receptor-like serine/threonine-specific protein kinase Rpg1

“…These results imply that the Avr proteins are secreted from haustoria into the extrahaustorial matrix and recognized by the intracellularly expressed L proteins, either by their translocation into the host cell or by interaction at the plasma membrane. The differential centrifugation procedure developed for Rpg1 can be applied to infected leaf segments and used to determine the proteins that bind with Rpg1 by using Blue native electrophoresis for isolation of membrane complexes (34,35) possibly by combination with cross-linking procedures for enzymatic active complexes (36). This procedure can supplement the yeast two-hybrid approach and is essential to identify both the avirulence protein and the initial components of the signal transduction chain activated by the Rpg1 protein.…”