Secretory proteins and glycoproteins from Paramecium cells

Secretory (glyco-)proteins released by exocytosis of trichocysts from Paramecium tetraurelia cells have been subfractionated into (a) insoluble components (trichocyst shafts) and (b) in components soluble in dilute buffer. Both fractions have been subjected to SDS-PAGE and blotting onto nitrocellulose sheets to determine binding of ConA. As in previous studies (on insoluble "trichocyst shafts"), fraction (a) contains the majority of proteins, with an M(r) range of 12-21 kDa in reducing conditions (+ mercaptoethanol, ME) and, in addition, of 29-38 kDa in non-reducing conditions (-ME). Two of these "trichynin" bands (M(r) = 31 and 35 kDa; -ME) strongly bind ConA. Insoluble fraction (a) also contains three non-reduceable protein bands of higher M(r) at 40, 76 and 78 kDa, all without any detectable glycosylation. The most prominent band (76 kDa) is observed both in fraction a and in fraction b, which contains the "soluble components". The most prominent bands (+ME) of fraction b are at 76, 110, 150-155 and ≥ 220 kDa, with less intense or variable bands at 58 and 45 kDa and additional bands at ≤ 21, 27-38, 40, 50, 53, 68, 100 and 180-190 kDa. It is unlikely that all bands with M(r) ≤ 38 kDa are trichynins or that bands with M(r) ≥ 220 kDa are surface antigen contaminants. The ≥ 220 kDa band also occurs, like most other bands, in "intact trichocysts" isolated with their membrane according to a new protocol. The 76,58 and 56 kDa bands of soluble material as well as some of the insoluble trichynin bands of 14, 31 and 35 kDa bind ConA. This correlates with our FITC-ConA labeling studies. The procedures used allow us to identify different molecular components of a highly organized secretory organelle, in which an isoluble protein matrix may provide a framework for the distinct arrangement and for the selective release of diffusible secretory constituents.