Cloning and Sequence Analysis of Genes Coding for Paramecium Secretory Granule (Trichocyst) Proteins
A UNIQUE PROTEIN FOLD FOR A FAMILY OF POLYPEPTIDES WITH DIFFERENT PRIMARY STRUCTURES (*)
- From the Centre de Génétique Moléculaire, Associated with the Université Pierre et Marie Curie, Centre National de la Recherche Scientifique, 91198 Gif-sur-Yvette, France
- ¶ Supported by a senior fellowship of the EEC Bridge Program and by a Poste Rouge from the CNRS. To whom correspondence should be addressed. Tel.: 33-1-69-82-43-92; Fax: 33-1-69-82-31-50.
Abstract
The architecturally complex secretory granules of Paramecium, known as trichocysts, have two unusual and seemingly contradictory features: their protein contents have crystalline organization (Sperling, L., Tardieu, A., and Gulik-Krzywicki, T.(1987) J. Cell Biol. 105, 1649-1662), yet these proteins are a heterogeneous set of molecules encoded by a large multigene family (Madeddu, L., Gautier, M.-C., Vayssié, L., Houari, A., and Sperling, L.(1995) Mol. Biol. Cell 6, 649-659). We present here the first complete sequences of three genes coding for three different precursors of the trichocyst crystalline matrix proteins. The deduced protein sequences indicate that each precursor gives rise to two of the mature polypeptides found in the crystalline trichocyst matrix. Analysis of putative processing sites suggests that a series of reactions, some of which may involve a novel endopeptidase, are involved in their proteolytic maturation. Each of the 6 mature polypeptides contains heptad segments. Characterization of the heptad segments leads us to propose that the mature polypeptides that compose the crystalline trichocyst matrix, despite their different primary structures, all share a unique protein fold, probably a 4 α-helical antiparallel bundle.
Footnotes
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↵§ Supported by a graduate fellowship from the Ministère de l'Enseignement Supérieure et de la Recherche (MESR).
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↵* This work was supported in part by the Genome Program of the Ministère de l'Enseignement Supérieure et de la Recherche (GIP GREG) and the CNRS. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by 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(™)/EMBL Data Bank with accession number(s) U47115, U47116, and U47117.
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↵1 The abbreviations used are:
- TMP
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trichocyst matrix protein
- MOPS
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morpholinopropanesulfonic acid
- PCR
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polymerase chain reaction
- kb
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kilobase(s)
- UWGCG
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University of Wisconsin Genetics Computer Group.
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↵2 F. Eisenhaber, F. Imperiale, P. Argos, and C. Froemmel, submitted for publication.
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↵3 The COILS program (27) calculates probabilities based on the statistical occurrence of amino acids in the different positions of a heptad repeat using a reference data base of 2 stranded, parallel coiled-coils from myosin, keratin, and tropomyosin.
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- Received November 20, 1995.
- Revision received February 21, 1996.
