Protein chemical characterization of Gc globulin (vitamin D-binding protein) isoforms; Gc-1f, Gc-1s and Gc-2

Maja Christiansen, Charlotte S Jørgensen, Inga Laursen, Daniel Hirschberg, Peter Højrup, Gunnar Houen

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Gc globulin, also called vitamin D-binding protein, is a plasma protein involved in the extracellular actin-scavenger system, vitamin D transport and possibly also other biological activities. Low levels of Gc globulin have been found to correlate with multiple organ failure and non-survival of patients with fulminant hepatic failure and trauma. Here, we characterize the dominant isoforms of plasma-derived Gc globulin from Cohn fraction IV paste with respect to amino acid sequence and posttranslational modifications. Gc globulin was purified in large scale and the isoforms separated by ion exchange chromatography. The separated isoforms and several commercial preparations of individual isoforms were characterized by mass spectrometry. This revealed that the major isoforms were non-glycosylated. Compared to the Gc-1f isoform the other dominating isoforms represented an Asp/Glu substitution (Gc-1s) and a Thr/Lys substitution (Gc-2) in agreement with DNA sequencing studies. The commercial preparations were found to represent mainly one or two isoforms. An O-linked glycan with a mass of 656 Da and terminating with a sialic acid residue was detected on a minor proportion of Gc globulin molecules.
Original languageEnglish
JournalBBA General Subjects
Volume1774
Issue number4
Pages (from-to)481-492
Number of pages11
ISSN0304-4165
DOIs
Publication statusPublished - 1. Apr 2007

Keywords

  • Chromatography, Ion Exchange
  • Electrophoresis, Polyacrylamide Gel
  • Glycosylation
  • Humans
  • Protein Isoforms
  • Spectrometry, Mass, Electrospray Ionization
  • Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
  • Vitamin D-Binding Protein

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