Phosphatidylserine

Phosphatidylserine

Components of phosphatidylserines: Blue, green: variable fatty acid groups Black: glycerol Red: phosphate Purple: serine
Identifiers
ChEBI	CHEBI:18303 Y
ChemSpider	none
DrugBank	DB00144 N
KEGG	C02737
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Phosphatidylserine (abbreviated Ptd-L-Ser or PS) is a phospholipid and is a component of the cell membrane.^[1] It plays a key role in cell cycle signaling, specifically in relation to apoptosis. It is a key pathway for viruses to enter cells via apoptotic mimicry.^[2] Its exposure on the outer surface of a membrane marks the cell for destruction via apoptosis.

Structure

Phosphatidylserine is a phospholipid—more specifically a glycerophospholipid—which consists of two fatty acids attached in ester linkage to the first and second carbon of glycerol and serine attached through a phosphodiester linkage to the third carbon of the glycerol.^[3]

Phosphatidylserine sourced from plants differs in fatty acid composition from that sourced from animals.^[4] It is commonly found in the inner (cytoplasmic) leaflet of biological membranes.^[5] It is almost entirely found in the inner monolayer of the membrane with only less than 10% of it in the outer monolayer.

Introduction

Phosphatidylserine (PS) is the major acidic phospholipid class that accounts for 13–15 % of the phospholipids in the human cerebral cortex.^[6] In the plasma membrane, PS is localized exclusively in the cytoplasmic leaflet where it forms part of protein docking sites necessary for the activation of several key signaling pathways. These include the Akt, protein kinase C (PKC) and Raf-1 signaling that is known to stimulate neuronal survival, neurite growth, and synaptogenesis.^{[7][8][9][10][11][12]} Modulation of the PS level in the plasma membrane of neurons has a significant impact on these signaling processes.

Biosynthesis

Biosynthesis of phosphatidylserine

Phosphatidylserine is formed in bacteria (such as E. coli) through a displacement of cytidine monophosphate (CMP) through a nucleophilic attack by the hydroxyl functional group of serine. CMP is formed from CDP-diacylglycerol by PS synthase. Phosphatidylserine can eventually become phosphatidylethanolamine by the enzyme PS decarboxylase (forming carbon dioxide as a byproduct).^[5] Similar to bacteria, yeast can form phosphatidylserine in an identical pathway.

In mammals, phosphatidylserine is instead derived from phosphatidylethanolamine or phosphatidylcholine through one of two Ca2+-dependent head-group exchange reactions in the endoplasmic reticulum. Both reactions require a serine but product an ethanolamine or choline, respectively. These are promoted by phosphatidylserine synthase 1 (PSS1) or 2 (PSS2).^[5] Conversely, phosphatidylserine can also give rise to phosphatidylethanolamine and phosphatidylcholine, although in animals the pathway to generate phosphatidylcholine from phosphatidylserine only operates in the liver.^[13]

Dietary sources

The average daily phosphatidylserine intake in a Western diet is estimated to be 130 mg.^[14] Phosphatidylserine may be found in meat and fish. Only small amounts are found in dairy products and vegetables, with the exception of white beans and soy lecithin. Phosphatidylserine is found in soy lecithin at about 3% of total phospholipids.^[15]

Table 1. Phosphatidylserine content in different foods.^[16]

Supplementation

References

External links

• DrugBank info page
• Phosphatidylserines at the US National Library of Medicine Medical Subject Headings (MeSH)