Worm Breeder's Gazette 1(2): 22

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Myofilament Proteins from C. elegans

H.E. Harris, H. Epstein

We have been working on the purification of native myofilament 
proteins from wild-type C.  elegans and have determined some of their 
biochemical and structural properties.  Procedures have been developed 
for isolating myosin, paramyosin, actin and tropomyosin at greater 
than 90% purity, from the same batch of worms.
Nematode myosin.  Our purified myosin is, presumably, a mixture of 
all nematode classes of myosin.  The properties described below 
therefore represent average properties of all myosins.  We are 
currently comparing the myosins of N2 with E190 and E675.  In E190, 
the concentration of unc 54 myosin seems insignificant, while E675 
contains an altered unc 54 product.
1) Besides the 210,000 heavy chains, it contains 2 light chain 
classes: 18,000 and 16,000 daltons.  Both classes are present in E190 
and E675.
2) The Ca2+-ATPase (10mM CaCl2) is comparable with rabbit skeletal 
muscle myosin.
3) The Mg2+-ATPase (2mM MgCl2 - 0.2mM CaCl2) is stimulated up to 
twofold by rabbit actin.  This activity is very labile.
4) The myosin forms either very long filaments with no apparent 
polarity, or short, very compact bipolar structures, when ionic 
strength is lowered to 0.1M in 10mM MgCl2.  The type of aggregate 
depends on whether the sample is precipitated slowly by dialysis, or 
rapidly by dilution.  Dialysis of nematode myosin and paramyosin 
together yields filaments with a paramyosin core and a surface coating 
of myosin.
Nematode tropomyosin.  This is unusual in having a higher molecular 
weight (40,000 by SDS gel electrophoresis) than has been reported for 
any other tropomyosin.  It forms paracrystals with a 38.0-39.0nm 
repeat, but a different molecular packing to rabbit skeletal muscle 
Calcium regulation of contraction in C.  elegans.  Activation of the 
ATPase of purified nematode myosin by rabbit actin is Ca2+-requiring.  
Similarly, activation of rabbit heavy meromyosin (calcium independent) 
by crude nematode thin filaments is stimulated 3-fold by Ca2+.  
Nematode muscle apparently contains both thick and thin filament 
linked calcium regulatory systems.