title: Heterogeneous N-terminal acylation of retinal proteins results from the retina's unusual lipid metabolism.
abstract: Protein N-myristoylation occurs by a covalent attachment of a C14:0 fatty acid to the N-terminal Gly residue. This reaction is catalyzed by a N-myristoyltransferase that uses myristoyl-coenzyme A as substrate. But proteins in the retina also undergo heterogeneous N-acylation with C14:2, C14:1, and C12:0 fatty acids. The basis and the role of this retina-specific phenomenon are poorly understood. We studied guanylate cyclase-activating protein 1 (GCAP1) as an example of retina-specific heterogeneously N-acylated protein. The types and the abundance of fatty acids bound to bovine retinal GCAP1 were C14:2, 37.0%; C14:0, 32.4%; C14:1, 22.3%; and C12:0, 8.3% as quantified by liquid chromatography coupled mass spectrometry. We also devised a method for N-acylating proteins in vitro and used it to modify GCAP1 with acyl moieties of different lengths. Analysis of these GCAPs both confirmed that N-terminal acylation of GCAP1 is critical for its high activity and proper Ca(2+)-dependent response and revealed comparable functionality for GCAP1 with acyl moieties of various lengths. We also tested the hypothesis that retinal heterogeneous N-acylation results from retinal enrichment of unusual N-myristoyltransferase substrates. Thus, acyl-coenzyme A esters were purified from both bovine retina and brain and analyzed by liquid chromatography coupled mass spectrometry. Substantial differences in acyl-coenzyme A profiles between the retina and brain were detected. Importantly, the ratios of uncommon N-acylation substrates--C14:2- and C14:1-coenyzme A to C14:0-coenzyme A--were higher in the retina than in the brain. Thus, our results suggest that heterogeneous N-acylation, responsible for expansion of retinal proteome, reflects the unique character of retinal lipid metabolism. Additionally, we propose a new hypothesis explaining the physiological relevance of elevated retinal ratios of C14:2- and C14:1-coenzyme A to C14:0-coenzyme A.
authors: Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965, USA.
authors: Grzegorz
authors: G
authors: Bereta
authors: Krzysztof
authors: K
authors: Palczewski
mesh_terms: D000214:Acyl Coenzyme A / Q000737:chemistry*; D000215:Acylation; D000818:Animals; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000737:chemistry; D002417:Cattle; D002645:Chickens; D002853:Chromatography, Liquid / Q000379:methods; D005227:Fatty Acids / Q000737:chemistry; D051604:Guanylate Cyclase-Activating Proteins / Q000737:chemistry; D050356:Lipid Metabolism; D013058:Mass Spectrometry / Q000379:methods; D051379:Mice; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012160:Retina / Q000378:metabolism*
chemical_list: D000214:Acyl Coenzyme A; D005227:Fatty Acids; D051604:Guanylate Cyclase-Activating Proteins; D002118:Calcium