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for pumping kinetics, but neither aspect has been ascertained. The mergence
of multiple isoforms of many proteins in Paramecium is explained by several
rounds of whole-genome duplications ( Aury et al., 2006 ).
2.3. Proteins required for membrane trafficking
Tables 9.1 and 9.2 summarize the protein inventory of the CVC in different
systems. Evidently current knowledge about molecular components of the
CVC is a patchwork, with information about widely different aspects from
the different cell
types
analyzed. Their comparison may promote
future analyses.
2.3.1 SNARE proteins
Alone, the reversible fusion/fission processes at the pore and at the CV/
radial arms connection call for SNARE proteins (soluble NSF
( N -ethylmaleimide sensitive factor) attachment protein receptors) and the
SNARE-specific chaperone, NSF. Surprisingly, only cursory information
exists apart from Paramecium . SNARE proteins are generally known to
mediate docking of a vesicle to a target membrane by formation of a
trans-complex and finally fusion ( Jahn and Fasshauer, 2012; Jahn and
Scheller, 2006 ). Depending on whether located at the vesicle or at the target
side, one differentiates between v-/R-SNAREs and t-/Q-SNAREs; R and
Q indicate the central amino acid in the a -helical SNARE domain. In Par-
amecium , several t-/Q-SNAREs and v-/R-SNAREs as well as NSF are
localized to the CVC. These CVC-resident SNAREs in P. tetraurelia
( Pt SNAREs) encompass the t-SNAREs Syntaxin2 (Syx), Syx14, and
Syx15 ( Kissmehl et al., 2007; Sch¨nemann et al., 2013 ) and the broadly dis-
tributed t-/Qab-SNARE type SNAP25-like protein (LP) ( Schilde et al.,
2008 ) as well as the v-/R-SNAREs Synaptobrevin2 (Syb), Syb6, and
Syb9 ( Schilde et al., 2006, 2010; Sch¨nemann et al., 2013 ). In Paramecium ,
synaptobrevins are actually longins, just as in plants ( Plattner, 2010a,b ).
Whole-cell-surface capacitance measurements have documented the
reversible detachment/reattachment of radial arms (with their ampullae)
during each pumping cycle of the CVC in Paramecium multimicronucleatum
( Grønlien et al., 2002; Tominaga and Allen, 1998 ). Here, NSF has been
localized in gently saponin permeabilized, surviving P. tetraurelia cells by
adding antibodies against species-specific NSF in presence of the inhibitor,
N -ethylmaleimide, and nonhydrolyzable ATP- g -S ( Kissmehl et al., 2002 ).
The occurrence of NSF and SNAREs over large parts of the CVC, par-
ticularly in the smooth spongiome, suggests the occurrence of many
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