The Chemorepulsive Activity of the Axonal Guidance Signal Semaphorin D Requires Dimerization*
- From Molekulare Neurogenetik, Abteilung Neurochemie, Max-Planck-Institut für Hirnforschung, Deutschordenstrasse 46, D-60528 Frankfurt/Main, Germany
Abstract
The axonal guidance signal semaphorin D is a member of a large family of proteins characterized by the presence of a highly conserved semaphorin domain of about 500 amino acids. The vertebrate semaphorins can be divided into four different classes that contain both secreted and membrane-bound proteins. Here we show that class III (SemD) and class IV semaphorins (SemB) form homodimers linked by intermolecular disulfide bridges. In addition to the 95-kDa form of SemD (SemD(95k)), proteolytic processing of SemD creates a 65-kDa isoform (SemD(65k)) that lacks the 33-kDa carboxyl-terminal domain. Although SemD(95k) formed dimers, the removal of the carboxyl-terminal domain resulted in the dissociation of SemD homodimers to monomeric SemD(65k). Mutation of cysteine 723, one of four conserved cysteine residues in the 33-kDa fragment, revealed its requirement both for the dimerization of SemD and its chemorepulsive activity. We suggest that dimerization is a general feature of sema- phorins which depends on class-specific sequences and is important for their function.
Footnotes
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↵* This work was supported by Deutsche Forschungsgemeinschaft Grant Pu102/4-1 and SFB 269.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.
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↵‡ Present address: EMBL, Meyerhofstrasse 1, D-69117 Heidelberg, Germany.
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↵§ To whom correspondence should be addressed. Fax: 49-69-96769-441; E-mail: pueschel{at}mpih-frankfurt.mpg.de.
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↵1 The abbreviations used are: SemD, semaphorin D; SemB, semaphorin B; SemD(65k) and SemD(95k), 65-kDa and 95-kDa isoforms of SemD, respectively; CTD, carboxyl-terminal domain; Fc, constant part of human immunoglobulin G1; PAGE, polyacrylamide gel electrophoresis; HEK, human embryonic kidney.
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↵2 A. W. Püschel, unpublished results.
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- Received August 27, 1997.
- Revision received November 17, 1997.
- The American Society for Biochemistry and Molecular Biology, Inc.
