Localisation and interactions of the Vipp1 protein in cyanobacteria

Abstract

The Vipp1 protein is essential in cyanobacteria and chloroplasts for the maintenance of photosynthetic function and thylakoid membrane architecture. To investigate its mode of action we generated strains of the cyanobacteria Synechocystis sp. PCC6803 and Synechococcus sp. PCC7942 in which Vipp1 was tagged with green fluorescent protein at the C-terminus and expressed from the native chromosomal locus. There was little perturbation of function. Live-cell fluorescence imaging shows dramatic relocalisation of Vipp1 under high light. Under low light, Vipp1 is predominantly dispersed in the cytoplasm with occasional concentrations at the outer periphery of the thylakoid membranes. High light induces Vipp1 coalescence into localised puncta within minutes, with net relocation of Vipp1 to the vicinity of the cytoplasmic membrane and the thylakoid membranes. Pull-downs and mass spectrometry identify an extensive collection of proteins that are directly or indirectly associated with Vipp1 only after high-light exposure. These include not only photosynthetic and stress-related proteins but also RNA-processing, translation and protein assembly factors. This suggests that the Vipp1 puncta could be involved in protein assembly. One possibility is that Vipp1 is involved in the formation of stress-induced localised protein assembly centres, enabling enhanced protein synthesis and delivery to membranes under stress conditions.

PilB localization correlates with the direction of twitching motility in the cyanobacterium Synechocystis sp. PCC 6803

“…2). Such a pattern of GFP localization is not observed in cells expressing free GFP, or in cells expressing other GFP-tagged proteins associated with the cytoplasmic membrane (Bryan et al, 2014). This indicates that the crescent-like distribution reflects a specific aspect of PilB1 behaviour.…”

IM30 triggers membrane fusion in cyanobacteria and chloroplasts

“…However, further studies have indicated that IM30 is involved in maintaining the structure and stability of internal membranes in chloroplasts and cyanobacteria, similar to its bacterial homologue PspA, and thus has a more protective function 27,28 . In addition, IM30 has been found to enhance protein translocation via the chloroplast Tat pathway 29 and involvement in photosystem biogenesis has been suggested 21,[30][31][32] . Currently, no model combining these diverse IM30 functions has been proposed, and the exact role of IM30 remains enigmatic.…”

Biogenesis of thylakoid membranes

“…Therefore, it has recently been suggested that VIPP1 is the major constituent of thylakoid centers [129]. Recent GFP-based live-cell imaging using confocal microscopy has revealed that, under low light conditions, VIPP1 is localized in a punctate manner preferentially at the cell periphery [53]. However, under high light levels, the number of punctate accumulations associated with internal thylakoid membranes increases substantially, suggesting a highly dynamic subcellular redistribution of VIPP1 under stress conditions (Chapter 21 [53,54]).…”

“…These include the VIPP1 protein, which is homologous to the bacterial phage shock protein PspA. VIPP1 has been implicated in thylakoid biogenesis and/or thylakoid maintenance in both cyanobacteria and chloroplasts [51][52][53]. The molecular details of VIPP1 functions are addressed in Chapter 21 [54] of this issue.…”