title: Endoplasmic reticulum microenvironment and conserved histidines govern ELOVL4 fatty acid elongase activity.
abstract: Autosomal dominant Stargardt-like macular dystrophy (STGD3) in humans results from mutations in elongation of very long chain FAs-like 4 (ELOVL4), which leads to vision loss in young adults. ELOVL4 is an integral endoplasmic reticulum (ER) protein that mediates the elongation of very long chain (VLC) FAs. Mutations in ELOVL4 lead to truncation and mislocalization of the translated protein from the ER, the site of FA elongation. Little is known about the enzymatic elongation of VLC-FAs by ELOVL4. We over-expressed full-length mouse ELOVL4, an N-glycosylation-deficient mutant, an ER-retention mutant, and mutants of active site histidines to parse their individual roles in VLC-FA elongation. ELOVL4 elongated appropriate precursors to the corresponding VLC-FA species ≥ 28 carbons. Active site histidine mutants of ELOVL4 did not elongate appropriate precursors, establishing ELOVL4 as the elongase. Displacing ELOVL4 from the ER was sufficient to cause loss of condensation activity, while absence of N-glycosylation was irrelevant for enzyme function. This study shows that ELOVL4 enzymatic activity is governed by individual histidines in its active site and the ER microenvironment, both of which are essential for elongation of VLC-FAs.
authors.affiliation: Departments of Cell Biology University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104.
authors.forename: Sreemathi
authors.initials: S
authors.lastname: Logan
authors.forename: Martin-Paul
authors.initials: MP
authors.lastname: Agbaga
authors.forename: Michael D
authors.initials: MD
authors.lastname: Chan
authors.forename: Richard S
authors.initials: RS
authors.lastname: Brush
authors.forename: Robert E
authors.initials: RE
authors.lastname: Anderson
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D020134:Catalytic Domain; D017124:Conserved Sequence; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D005136:Eye Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism*; D015870:Gene Expression; D006031:Glycosylation; D057809:HEK293 Cells; D006367:HeLa Cells; D006639:Histidine / Q000737:chemistry; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D016297:Mutagenesis, Site-Directed; D011499:Protein Processing, Post-Translational; D021381:Protein Transport
chemical_list: C498834:Elovl4 protein, mouse; D005136:Eye Proteins; D005227:Fatty Acids; D008565:Membrane Proteins; D006639:Histidine
keywords: autosomal dominant; elongation of very long chain fatty acids-like 4; lipid metabolism; mutant; retinal degeneration