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Glycobiology Advance Access published online on May 18, 2005
Glycobiology, doi:10.1093/glycob/cwi077
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© The Author 2005. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oupjournals.org
Received March 4, 2005
Revised May 9, 2005
Accepted May 10, 2005

Article

O-linked Glycosylation in Maize-Expressed Human IgA1

Anton S. Karnoup 1*, Virgil Turkelson 1, and W.H. Kerr Anderson 2

1 The Dow Chemical Company, Analytical Sciences, 1897 Bldg., Midland, MI 48667,USA
2 The Dow Chemical Company, Dow Biopharma, 1707 Bldg., Midland, MI 48674, USA

* To whom correspondence should be addressed.
Anton S. Karnoup, E-mail: ASKarnoup{at}dow.com


  Abstract

O-linked glycans vary between eukaryotic cell types and play an important role in determining a glycoprotein’s properties, including stability, target recognition, and potentially immunogenicity. We describe O-linked glycan structures of a recombinant human IgA1 (hIgA1) expressed in transgenic maize. Up to six proline/hydroxyproline conversions and variable amounts of arabinosylation (Pro/Hyp+Ara) were found in the hinge region of maize-expressed hIgA1 heavy chain (HC) using a combination of MALDI MS, chromatography, and amino acid analysis. Approximately 90% of hIgA1 was modified in this way. An average molar ratio of six Ara units per molecule of hIgA1 was revealed. Substantial sequence similarity was identified between the HC hinge region of hIgA1 and regions of maize extensin-family of hydroxyproline-rich glycoproteins (HRGP). We propose that due to this sequence similarity, the HC hinge region of maize-expressed hIgA1 can become a substrate for post-translational conversion of Pro to Hyp by maize prolyl-hydroxylase(s) with the subsequent arabinosylation of the Hyp residues by Hyp-glycosyltransferase(s) in the Golgi apparatus in maize endosperm tissue. The observation of up to six Pro/Hyp hydroxylations combined with extensive arabinosylation in the hIgA1 HC hinge-region is well in agreement with the Pro/Hyp hydroxylation model and the Hyp contiguity hypothesis suggested earlier in literature for plant HRGPs. For the first time the extensin-like Hyp/Pro conversion and O-linked arabinosylation are described for a recombinant therapeutic protein expressed in transgenic plants. Our findings are of significance to the field of plant biotechnology and biopharmaceutical industry developing transgenic plants as a platform for production of recombinant therapeutic proteins.

Keywords: O-glycosylation, IgA1 antibody, maize, HRGP, mass spectrometry.
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