Phospholipases remodeling

In some cases the functions of phospholipases in cells are purely degradative and result in the release of the phospholipid components (fatty acids, glycerol, phosphate, and head-groups). But in many cases phospholipases have important roles in synthesis and regulation. For example, we have seen how phospholipase A2 catalyzes the first step in the remodeling of phosphatidylcholine to the surfactant... 

Zavaleta-Pastor, M., Sohlenkamp, C., Gao, J.-L., Guan, Z., Zaheer, R., Finan, T.M., Raetz, C.R.H., Lopez-Lara, I.M., Geiger, O. Sinorhizobiummeliloti phospholipase C required for lipid remodeling during phosphorus limitation. Proc Natl Acad Sci USA 107 (2010) 302-307. 

Phospholipid synthesis occurs in the membrane of the SER. After phospholipids are synthesized, they are remodeled by altering their fatty acid composition. Phospholipid degradation is catalyzed by several phospholipases. 

Most of the reactions involved in lipid biosynthesis appear to be located in the smooth endoplasmic reticulum (SER), although several enzyme activities have also been detected in the Golgi complex. Because each enzyme is a membrane-associated protein with its active site facing the cytoplasm, the biosynthesis of phospholipid occurs at the interface of ER membrane and cytoplasm. The fatty acid composition of phospholipids changes somewhat after their synthesis. (Typically, unsaturated fatty acids replace the original saturated fatty acids incorporated during synthesis.) Most of this remodeling is accomplished by certain phospholipases and acyl transferases. Presumably, this process allows a cell to adjust the fluidity of its membranes. 

After phospholipids are synthesized at the interface of the SER and the cytoplasm, they are often remodeled, that is, their fatty acid composition is adjusted. The turnover (i.e., the degradation and replacement) of phospholipids, mediated by the phospholipases, is rapid. 

Flip-flopping between leaflets, lateral diffusion, and membrane fusion and fission are not the only dynamic processes of phospholipids In membranes. Their fatty acyl chains and. In some cases, their head groups are subject to ongoing covalent remodeling (e.g., hydrolysis of fatty esters by phospholipases and resynthesIs by acyl transferases). Another key... 

Fig. 11. Proposed pathway for remodeling of diphosphatidylglycerol (DPG) (cardiolipin). PLAj, phospholipase Aj PC, phosphatidylcholine FA, fatty acid. Tafazzin catalyzes the reacylation of monolyso-DPG with linoleoyl-CoA being the preferred acyl-CoA.

Balsinde J, Bianco I, Ackermann EJ, Conde-Frieboes K, Dennis EA. Inhibition of calcium-independent phospholipase A2 prevents arachidonic acid incorporation and phospholipid remodeling in P3881Di macrophages. Proc Natl Acad Sci USA 1995 92 8527-8531. 

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