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J. Biol. Chem., Vol. 276, Issue 14, 11113-11125, April 6, 2001
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From the Biochemistry Laboratory, The Institute of Low Temperature
Science, Hokkaido University, Sapporo 060-0819, Japan
Pro-phenoloxidase (proPO) in insects is activated
through the action of a protease cascade triggered by minute amounts of microbial cell wall components. It is an important molecule for the
defense against invading microorganisms and for the repair of wounds.
In the accompanying paper (Asano, T., and Ashida, M. (2001)
J. Biol. Chem. 276, 11100-11112), a proPO isoform,
proPO-HS, in the hemolymph of the silkworm, Bombyx mori, is
reported to be transported to the cuticle. The transported proPO
isoform was recovered from the cuticle and named proPO-CS. The elution
profiles of proPO-CS and proPO-HS in reversed-phase high performance
liquid chromatography (HPLC) were found to be different, giving a basis to the inference that proPO-CS is a modified form of proPO-HS. In the
present study, we investigated the nature of the modifications occurring in proPO-CS, in which proteolytically and chemically cleaved
fragments originating from the subunits of proPO-CS and proPO-HS were
analyzed by reversed-phase HPLC, amino acid sequencing, and mass
spectrometry. A subunit of the heterodimeric proPO-CS was found to
contain five or six methionine sulfoxides, and another subunit was
found to contain one methionine residue oxidized to the sulfoxide. All
of the oxidized methionyl residues were identified. Other than
oxidation of the methionyl residues, no additional modification of
proPO-CS was found. In the model structure of each subunit of proPO-CS
constructed by protein modeling with the known structures of the
horseshoe crab, Limulus polyphemus, hemocyanin type II
subunit as templates, the methionine residues identified as methionine
sulfoxide had high degrees of accessibility to the solvent. The
implication of the oxidation at the methionine residues is discussed in
relation to the mechanism of transepithelial transport of proPO from
the hemolymph to the cuticle.
Transepithelially Transported Pro-phenoloxidase in the
Cuticle of the Silkworm, Bombyx mori
IDENTIFICATION OF ITS METHIONYL RESIDUES OXIDIZED TO METHIONINE
SULFOXIDES*
*
This work was supported in part by Grants 09265201 and
06454023 from the Japan Ministry of Education, Science, Sports, and Culture.The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
To whom correspondence should be addressed. Tel.:
81-11-706-6877; Fax: 81-11-706-7142; E-mail:
ashida@pop.lowtem.hokudai.ac.jp.
This article has been cited by other articles:
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T. Asano and M. Ashida Cuticular Pro-phenoloxidase of the Silkworm, Bombyx mori. PURIFICATION AND DEMONSTRATION OF ITS TRANSPORT FROM HEMOLYMPH J. Biol. Chem., March 30, 2001; 276(14): 11100 - 11112. [Abstract] [Full Text] [PDF] |
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T. Nagai, T. Osaki, and S.-i. Kawabata Functional Conversion of Hemocyanin to Phenoloxidase by Horseshoe Crab Antimicrobial Peptides J. Biol. Chem., July 13, 2001; 276(29): 27166 - 27170. [Abstract] [Full Text] [PDF] |
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