title: Direct analysis of VLDL by TOF-MS allows rapid definition of Apo E genotypes and facilitates characterisation of post translational changes.
abstract: BACKGROUND
  Apolipoprotein E (Apo E) is a glycoprotein which acts as a ligand facilitating the uptake of lipids. Three common isoforms of Apo E are recognised, E2, E3 and E4. E2 and E4 are associated with altered lipid metabolism and increased cardiovascular risk. We report a novel variant of Apo E (c.382G>A) predicting 110Asp→Asn identified by genotyping, we were prompted to investigate this further as the amino acid substitution produced a prospective N-glycosylation site in this novel variant.
  
  
  METHODS
  We present a new rapid approach to genotyping Apo E performed by electrospray TOF-MS, on the same sample analysed by ultracentrifugation. The analysis can be performed in <10min and requires minimal sample volume. Control samples were used to verify the analysis.
  
  
  RESULTS
  Spectra showed the expected mass for the E3 isoform at 34,237Da, E2 and E4 isoforms were identifiable by peaks at -53Da and +53Da respectively. Post translational glycosylation of the protein can also be identified. The novel isoform had a mass of 34,237Da without evidence of N-glycosylation. No significant effect on lipid metabolism was identified.
  
  
  CONCLUSIONS
  The electrospray TOF-MS approach potentially provides a rapid alternative method for genotyping Apo E and for the investigation of novel isoforms.
authors.affiliation: Canterbury Health Laboratories, P.O Box 151, Christchurch, New Zealand; Pathology Department, University of Otago, School of Medicine, Christchurch, New Zealand. Electronic address: richard.king@cdhb.health.nz.
authors.forename: Richard I
authors.initials: RI
authors.lastname: King
authors.affiliation: Canterbury Health Laboratories, P.O Box 151, Christchurch, New Zealand; Pathology Department, University of Otago, School of Medicine, Christchurch, New Zealand. Electronic address: steve.brennan@otago.ac.nz.
authors.forename: Stephen O
authors.initials: SO
authors.lastname: Brennan
mesh_terms: D001057:Apolipoproteins E / Q000235:genetics*; D005838:Genotype; D006801:Humans; D008079:Lipoproteins, VLDL / Q000097:blood*; D011499:Protein Processing, Post-Translational; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D001057:Apolipoproteins E; D008079:Lipoproteins, VLDL
keywords: Apolipoprotein E; Dyslipidaemia; N-glycosylation; Post translational modification; Whole protein mass spectrometry