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
Mc. Gautier et al., 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, The Journal of biological chemistry, 271(17), 1996, pp. 10247-10255
The architecturally complex secretory granules of Paramecium, known as
trichocysts, have two unusual and seemingly contradictory features: t
heir protein contents have crystalline organization (Sperling, L., Tar
dieu, 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., Vayssie, L., Hou
ari, A., and Sperling, L. (1995) Mol. Biol. Cell 6, 649-659). We prese
nt here the first complete sequences of three genes coding for three d
ifferent 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 mat
rix. Analysis of putative processing sites suggests that a series of r
eactions, some of which may involve a novel endopeptidase, are involve
d in their proteolytic maturation. Each of the 6 mature polypeptides c
ontains heptad segments. Characterization of the heptad segments leads
us to propose that the mature polypeptides that compose the crystalli
ne trichocyst matrix, despite their different primary structures, all
share a unique protein fold, probably a 4 alpha-helical antiparallel b
undle.