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Phasins, Multifaceted Polyhydroxyalkanoate Granule-Associated Proteins.

ABSTRACT: 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.

SUBMITTER: Mezzina MP

PROVIDER: S-EPMC4988190 | biostudies-literature | 2016 Sep

REPOSITORIES: biostudies-literature

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Phasins, Multifaceted Polyhydroxyalkanoate Granule-Associated Proteins.

Mezzina Mariela P MP Pettinari M Julia MJ

Applied and environmental microbiology 20160815 17

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 α-helix comp ...[more]

PMID: 27287326

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Project description:Poly(3-hydroxybutyrate) (PHB) granules are covered by a surface layer consisting of mainly phasins and other PHB granule-associated proteins (PGAPs). Phasins are small amphiphilic proteins that determine the number and size of accumulated PHB granules. Five phasin proteins (PhaP1 to PhaP5) are known for Ralstonia eutropha. In this study, we identified three additional potential phasin genes (H16_B1988, H16_B2296, and H16_B2326) by inspection of the R. eutropha genome for sequences with "phasin 2 motifs." To determine whether the corresponding proteins represent true PGAPs, fusions with eYFP (enhanced yellow fluorescent protein) were constructed. Similar fusions of eYFP with PhaP1 to PhaP5 as well as fusions with PHB synthase (PhaC1), an inactive PhaC1 variant (PhaC1-C319A), and PhaC2 were also made. All fusions were investigated in wild-type and PHB-negative backgrounds. Colocalization with PHB granules was found for all PhaC variants and for PhaP1 to PhaP5. Additionally, eYFP fusions with H16_B1988 and H16_B2326 colocalized with PHB. Fusions of H16_B2296 with eYFP, however, did not colocalize with PHB granules but did colocalize with the nucleoid region. Notably, all fusions (except H16_B2296) were soluble in a ΔphaC1 strain. These data confirm that H16_B1988 and H16_B2326 but not H16_B2296 encode true PGAPs, for which we propose the designation PhaP6 (H16_B1988) and PhaP7 (H16_B2326). When localization of phasins was investigated at different stages of PHB accumulation, fusions of PhaP6 and PhaP7 were soluble in the first 3 h under PHB-permissive conditions, although PHB granules appeared after 10 min. At later time points, the fusions colocalized with PHB. Remarkably, PHB granules of strains expressing eYFP fusions with PhaP5, PhaP6, or PhaP7 localized predominantly near the cell poles or in the area of future septum formation. This phenomenon was not observed for the other PGAPs (PhaP1 to PhaP4, PhaC1, PhaC1-C319A, and PhaC2) and indicated that some phasins can have additional functions. A chromosomal deletion of phaP6 or phaP7 had no visible effect on formation of PHB granules.

Project description:BackgroundA G4C2 hexanucleotide repeat expansion in the noncoding region of C9orf72 is the major genetic cause of frontotemporal dementia and amyotrophic lateral sclerosis (c9FTD/ALS). Putative disease mechanisms underlying c9FTD/ALS include toxicity from sense G4C2 and antisense G2C4 repeat-containing RNA, and from dipeptide repeat (DPR) proteins unconventionally translated from these RNA products.MethodsIntracerebroventricular injections with adeno-associated virus (AAV) encoding 2 or 149 G4C2 repeats were performed on postnatal day 0, followed by assessment of behavioral and neuropathological phenotypes.ResultsRelative to control mice, gliosis and neurodegeneration accompanied by cognitive and motor deficits were observed in (G4C2)149 mice by 6?months of age. Recapitulating key pathological hallmarks, we also demonstrate that sense and antisense RNA foci, inclusions of poly(GA), poly(GP), poly(GR), poly(PR), and poly(PA) DPR proteins, and inclusions of endogenous phosphorylated TDP-43 (pTDP-43) developed in (G4C2)149 mice but not control (G4C2)2 mice. Notably, proteins that play a role in the regulation of stress granules - RNA-protein assemblies that form in response to translational inhibition and that have been implicated in c9FTD/ALS pathogenesis - were mislocalized in (G4C2)149 mice as early as 3?months of age. Specifically, we observed the abnormal deposition of stress granule components within inclusions immunopositive for poly(GR) and pTDP-43, as well as evidence of nucleocytoplasmic transport defects.ConclusionsOur in vivo model of c9FTD/ALS is the first to robustly recapitulate hallmark features derived from both sense and antisense C9orf72 repeat-associated transcripts complete with neurodegeneration and behavioral impairments. More importantly, the early appearance of persistent pathological stress granules prior to significant pTDP-43 deposition implicates an aberrant stress granule response as a key disease mechanism driving TDP-43 proteinopathy in c9FTD/ALS.

Dataset Information

Phasins, Multifaceted Polyhydroxyalkanoate Granule-Associated Proteins.

Publications

Phasins, Multifaceted Polyhydroxyalkanoate Granule-Associated Proteins.

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