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J. Biol. Chem., Vol. 282, Issue 42, 30381-30392, October 19, 2007

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The Chaotrope-soluble Glycoprotein GP2 Is a Precursor of the Insoluble Glycoprotein Framework of the Chlamydomonas Cell Wall^*

Jürgen Voigt¹, Johannes Woestemeyer, and Ronald Frank^¶

From the Institute for Biochemistry, University of Leipzig, Johannisallee 30, D-04103 Leipzig, Germany, the Institute for Microbiology, Friedrich Schiller University, Neugasse 24, D-07743 Jena, Germany, and the ^¶Department of Chemical Biology, Helmholtz Centre for Infection Research, Inhoffenstrasse 7, D-38124 Braunschweig, Germany

The cell wall of the unicellular green alga Chlamydomonas reinhardtii consists of an insoluble, hydroxyproline-rich glycoprotein framework and several chaotrope-soluble, hydroxyproline-containing glycoproteins. Up to now, there have been no data concerning the amino acid sequences of the hydroxyproline-containing polypeptides of the insoluble wall fraction. Matrix-assisted laser desorption ionization time-of-flight analyses of peptides released from the insoluble cell wall fraction by trypsin treatment revealed the presence of 14 peptide fragments that could be attributed to non-glycosylated domains of the chaotrope-soluble cell wall glycoprotein GP2. However, these peptides cover only 15% of the GP2 polypeptide backbone. Considerably more information concerning the presence of GP2 in the insoluble cell wall fraction was obtained by an immunochemical approach. For this purpose, 407 overlapping pentadecapeptides covering the whole known amino acid sequence of GP2 were chemically synthesized and probed with a polyclonal antibody raised against the deglycosylated, insoluble cell wall fraction. This particular antibody reacted with 297 of the 407 GP2-derived peptides. The peptides that were recognized by this antibody are distributed over the whole known GP2 sequence. The epitopes recognized by polyclonal antibodies raised against the 64- and 45-kDa constituents purified from the deglycosylation products of the insoluble cell wall fraction are also distributed over the whole GP2 backbone, although the corresponding antigens are considerably smaller than GP2. The significance of the latter results for the structure of the insoluble cell wall fraction is discussed.

Received for publication, February 26, 2007 , and in revised form, August 1, 2007.

^* This work was supported by Deutsche Forschungsgemeinschaft Grant VO 327/3. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. The nucleotide sequence(s) reported in this paper has been submitted to the GenBank^TM/EBI Data Bank with accession number(s) BN001086 and AM419024 [GenBank] .

¹ To whom correspondence should be addressed. Tel.: 49-341-972-2141; Fax: 49-341-972-2109; E-mail: juergen.voigt{at}medizin.uni-leipzig.de.

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