Biosynthesis and physiological functions of N-acyl amino acids
Abstract: N-acyl amino acids are lipid signalling molecules that have recently been identified in biological systems. These lipids are structurally related to the endocannabinoids, although they do not activate cannabinoid receptors. In 2001, N-arachidonoyl glycine was the first signalling lipid in this group to be identified in bovine and rat brain and since then, about 50 novel N-acyl amino acids have been identified in mammalian systems. These N-acyl amino acids are involved in regulating pain processes, are anti-inflammatory and regulate body temperature, but the metabolic pathways for production and metabolism remain poorly understood.This thesis focussed on the identification of pathways for production and regulation of N-acyl amino acids, in particular N-acyl glycines, and in identifying physiological functions for N-acyl amino acids (particularly N-acyl taurines). Our results identified an enzymatic pathway for production of N-acyl glycines in human and we identified that the human glycine N-acyltransferase-like 2 (hGLYATL2) conjugates (amidates) medium- and long-chain, saturated and unsaturated acyl-CoAs with glycine, to produce N-acyl glycines, with the preferential production of N-oleoyl glycine. Furthermore, we have characterized two other members of the gene family of glycine N-acyltransferases (GLYATs) in human, the hGLYATL1 and hGLYATL3 that may be involved in the production of N-acyl amino acids.As N-acyl glycines are bioactive signalling molecules, it is likely their production requires a rapid on/off switch. The post-translational modification of proteins can result in enzyme regulation, without the need for transcriptional regulation. We have identified that hGLYATL2 is regulated by acetylation/deacetylation on lysine 19, and using mutation analysis, we show that deacetylation of lysine 19 is important for full enzyme activity.The physiological functions of N-acyl amino acids are not well studied to date. In this thesis, we have identified that N-arachidonoyl taurine and N-oleoyl taurine trigger insulin secretion by increasing the calcium flux in pancreatic b-cells via the activation of transient receptor potential vanilloid subfamily 1 (TRPV1).This work on N-acyl amino acids has led us to identify new pathways and physiological functions for these lipid signalling molecules, which advances our knowledge of the importance of these lipids in mammalian systems.
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