Friday, May 28, 2010

Peroxisome-Lipid bodies Romance

(Note - Lipid bodies are also known as Lipid Droplets LDs )
Peroxisomes interact with various organelles like ER, mitochondria, chloroplast which involves proteins as well as various metabolite transport. Lipid bodies are intracellular cytoplasmic triacylglycerol storage sites in cells like adipocytes. Recently much insight has been gained into protein components of lipid droplets and interaction of LDs with other organelles, especially with peroxisomes. Peroxisomes and mitochondria are involved in fatty acid beta oxidation so naturally, the lipids are mobilized from LDs and further metabolized in other organelles as energy source.

Many viruses are known to use distinct organelles as a site for their localization and replicative proliferation. For e.g. Hepatitis C virus on lipid bodies (McLauchlan J, 2009) and Tomato bushy stunt virus (TBSV) on peroxisome membrane in plants (McCartney AW et al., 2005). Indeed many viruses employ the strategy where viral genome encodes pathogenicity factors with targeting signals for the host organelle. This is hot topic thesedays due to availability of viral genomes as well as understanding of organelle targeting signals.(See the related event at end of the post).
A new paper has been accepted in The Plant Journal (2008 Impact Factor - 6.493, Source - Journal Homepage) titled “The AtCPK1 Calcium-dependent Protein Kinase mediates pathogen resistance in Arabidopsis. (Click here to see abstract)
"Accepted Article" , The Plant Journal , Online published - 18 May 2010

Lipid bodies perform crucial roles in plants, most interestingly in Seeds where energy stored in form of lipids is utilized during germination. Since much is known about LDs in mammals due to their importance in cardiovascular diseases, Plant LD remain relatively less explored. In this paper authors have unraveled a protein in Arabidopsis which is dually localized on lipid bodies and peroxisomes. Calcium-dependent Protein Kinase from Arabidopsis thaliana (AtCPK) was analyzed. AtCPK1 is shown to be involved in innate immunity of plants against various pathogens. Authors have also deduced that the pathway involved in CPK mediated immunity is Salicylic Acid (SA) dependent signalling pathway leading to expression of disease resistance genes.

In recent "Cell" paper by it was shown that Peroxisomes play important role in innate immunity against Viral infections through dually localized protein MAVS on mitochondria and peroxisomes (Dixit et al, 2010). Peroxisome localized MAVS elicits Interferon independent gene response and impart immediate but short term protection and mitochondrial MAVS giving delayed but longer INF-dependant gene expression response. Thus complementing activities of the two organelles is necessary for sustained immune response (Dixit et al, 2010).
Similarly in plants, AtCPK1 is shown to be localized to both organelles Lipid bodies and peroxisome and are involved in plant immune response against pathogens which involves Salicylic acid signalling pathway as demonstrated by authors in this paper.

The peroxisomes now gain centre stage as a functional entity involved in not mere free radical detoxification or fatty acid metabolism but in life saving Immune responses. In both cases of plants and humans, the actual cascade of immune response originating from peroxisomal part remains to be deduced in future studies
Related Event -
Talk by Prof. Dr. Sigrun Reumann
“Identification of peroxisome-targeted pathogen defense proteins by new subcellular targeting prediction algorithms”
Details - Click Here

(Note - All peroxisome related events can be found under “Events Tab” on this blog, customized in a calendar. But I will also post the events related to the specific topic in the blogpost itself.) 

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