The Ralstonia eutropha H16 phasin PhaP1 is targeted to intracellular triacylglycerol inclusions in Rhodococcus opacus PD630 and Mycobacterium smegmatis mc2155, and provides an anchor to target other proteins

Hänisch, Jan; Wältermann, Marc; Robenek, Horst; Steinbüchel, Alexander

doi:10.1099/mic.0.28969-0

Cited by 37 publications

(22 citation statements)

References 38 publications

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“…We are also interested in the possibility that the network may on May 11, 2018 by guest http://jb.asm.org/ provide a focal point where proteins can transiently associate to mediate cellular/PHA reactions. This is suggested by recent studies in which it has been shown that phasins (PhaP) perform this function for triacylglycerol inclusions (11). It is also of interest that the 25-amino-acid, alanine-rich carboxy terminus of PhaP exhibits minor homology to the mouse clathrin coat assembly protein (GenBank accession number Q61548), a membrane-embedded protein that can recruit and release clathrin and other proteins (12).…”

Section: Discussionmentioning

confidence: 93%

PhaP Is Involved in the Formation of a Network on the Surface of Polyhydroxyalkanoate Inclusions in Cupriavidus necator H16

et al. 2008

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Polyhydroxyalkanoate (PHA) inclusions are polymeric storage inclusions formed in some bacterial species when carbon levels are high but levels of another essential nutrient, such as nitrogen, are low. Though much is known about PHA synthesis, little is known about inclusion structure. In this study, atomic force microscopy (AFM) was employed to elucidate the structure of PHA inclusions at the nanoscale level, including the characterization of different layers of structure. AFM data suggest that underneath the inclusion envelope, there is a 2-to 4-nm-thick network layer that resides on top of a harder layer that is likely to be a crystalline lamellar polymer. The network is comprised of ϳ20-nm-wide linear segments and junctions that are typically formed by the joining of three to four of the linear segments. In some cases, ϳ50-nm globular structures that are raised ϳ1 to 2 nm above the network are present at the junctions. These globular structures always have a central pore that is ϳ15 nm in diameter. To determine if the major surface protein of PHA inclusions, PhaP, is involved in the structure of this network, inclusions from Cupriavidus necator H16 ⌬phaP were examined. No network structure was detected. Instead, apparently random globular structures were found on the surfaces of the inclusions. When PhaP levels were reconstituted in this strain by the addition of phaP on a plasmid, the network was also reconstituted, albeit in a slightly different arrangement from that of the wild-type network. We conclude that PhaP participates in the formation of the inclusion network.

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Section: Discussionmentioning

confidence: 93%

PhaP Is Involved in the Formation of a Network on the Surface of Polyhydroxyalkanoate Inclusions in Cupriavidus necator H16

et al. 2008

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“…Investigation of other PHA-accumulating bacteria revealed that all of them have small proteins (phasins) attached to the surface layer of PHA granules (119). Expression of PhaP in triacylglycerol-accumulating bacteria showed that PhaP is able to bind to oil droplets in vivo (27,116). At present, it is not known whether phospholipids detected in isolated nPHB granules are also in vivo components of the granule surface layer or whether they represent an experimental artifact during cell extract preparation.…”

Section: Phasins (Phaps) and Pharmentioning

confidence: 97%

Polyhydroxyalkanoate Granules Are Complex Subcellular Organelles (Carbonosomes)

2009

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Polyhydroxyalkanoates (PHAs) such as poly(3-hydroxybutyrate) (PHB) or poly(3-hydroxyoctanoate), are universal prokaryotic storage compounds of carbon and energy. PHAs are accumulated intracellularly in form of inclusion bodies (PHA granules) during times of oversupply with carbon sources (for reviews, see references 2, 54, 64, 76, 86, and 100). PHAs can consist of short-chain-length hydroxyalkanoic acids (PHA SCL ) or medium-chain-length monomers (PHA MCL ), depending on strain and culture conditions. Given a number of more than 150 identified hydroxyalkanoates as potential constituents (101) the theoretical number of different PHA copolymers is incredibly high. A few PHAs, such as PHB and copolymers of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate, and/or 4-hydroxybutyrate, are produced by industry (Biocycle, Biomer, Biopol, Enmat, Mirel, and Nodax).The number of publications on PHA metabolism has considerably increased in the last two decades, and many aspects of the biosynthesis, molecular architecture, intracellular mobilization, extracellular degradation, and commercial applications of PHAs have been addressed. One exiting outcome of these studies was the finding that many polypeptides are specifically present on the surface of PHA granules, much more than would be essential for PHA synthesis. These proteins constitute a particular surface layer on PHA granules that is essential for PHA metabolism. In conclusion, PHA granules are complexly organized subcellular structures and appear to be more than simple polymer inclusions. The current knowledge of the biochemical functions of PHA-associated proteins will be reviewed here. This will be done using the example of Ralstonia eutropha H16, which is the model organism of PHA research and has become an important prokaryotic strain for several biotechnological applications (82). It should be noted that several other taxonomic names of R. eutropha are found in literature. These include Hydrogenomonas eutropha, Alcaligenes eutrophus, Wautersia eutropha, and Cupriavidus necator. We used here the most commonly accepted name, R. eutropha, which has been also used for description of the recently sequenced genome (71). When appropriate, the properties of PHA-bound proteins of other organisms are discussed afterward. PHA SYNTHASESPHA synthase is the key enzyme of PHA synthesis and catalyzes the polymerization of hydroxyacyl-coenzyme A (CoA) to PHA and free CoA. The first PHA synthase gene (phaC) was cloned 20 years ago. Remarkably, this was done independently in three labs with the same bacterial strain, R. eutrophus H16 (66, 95, 97). Meanwhile, several PHA synthases from different sources have been biochemically investigated, and many more PHA synthase genes have been cloned or have been determined by genome sequencing. PHA synthases currently are divided into four classes depending on their subunit composition and substrate specificity. The R. eutropha and Pseudomonas putida (previously Pseudomonas oleovorans) PHA synthases represent class I (producing PHA SCL ) and class ...

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“…This protein has been observed to interact with granules containing both PHA and triacylglycerols in R. ruber (24), so its characteristics might be associated with the particular composition of the lipid granules accumulated by this oleaginous bacterium. However, phasins that lack clear hydrophobic domains, such as PhaP Re , have been observed to bind to triacylglycerol inclusions when expressed in R. opacus and Mycobacterium smegmatis (25). Amphipathic helices in phasins might be important not only for the interactions of these proteins with the polymer but also for interactions with other granule-associated proteins and with hydrophobic regions of misfolded proteins and inclusion bodies (IBs) (23).…”

Section: Interaction With Pha Granulesmentioning

confidence: 99%

Phasins, Multifaceted Polyhydroxyalkanoate Granule-Associated Proteins

Mezzina

Pettinari

2016

Appl Environ Microbiol

101

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Phasins are the major polyhydroxyalkanoate (PHA) granule-associated proteins. They promote bacterial growth and PHA synthesis and affect the number, size, and distribution of the granules. These proteins can be classified in 4 families with distinctive characteristics. Low-resolution structural studies and in silico predictions were performed in order to elucidate the structure of different phasins. Most of these proteins share some common structural features, such as a preponderant ␣-helix composition, the presence of disordered regions that provide flexibility to the protein, and coiled-coil interacting regions that form oligomerization domains. Due to their amphiphilic nature, these proteins play an important structural function, forming an interphase between the hydrophobic content of PHA granules and the hydrophilic cytoplasm content. Phasins have been observed to affect both PHA accumulation and utilization. Apart from their role as granule structural proteins, phasins have a remarkable variety of additional functions. Different phasins have been determined to (i) activate PHA depolymerization, (ii) increase the expression and activity of PHA synthases, (iii) participate in PHA granule segregation, and (iv) have both in vivo and in vitro chaperone activities. These properties suggest that phasins might play an active role in PHA-related stress protection and fitness enhancement. Due to their granule binding capacity and structural flexibility, several biotechnological applications have been developed using different phasins, increasing the interest in the study of these remarkable proteins.

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The Ralstonia eutropha H16 phasin PhaP1 is targeted to intracellular triacylglycerol inclusions in Rhodococcus opacus PD630 and Mycobacterium smegmatis mc2155, and provides an anchor to target other proteins

Cited by 37 publications

References 38 publications

PhaP Is Involved in the Formation of a Network on the Surface of Polyhydroxyalkanoate Inclusions in Cupriavidus necator H16

PhaP Is Involved in the Formation of a Network on the Surface of Polyhydroxyalkanoate Inclusions in Cupriavidus necator H16

Polyhydroxyalkanoate Granules Are Complex Subcellular Organelles (Carbonosomes)

Phasins, Multifaceted Polyhydroxyalkanoate Granule-Associated Proteins

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