Worm Breeder's Gazette 14(1): 39 (October 1, 1995)

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.

Three-Dimensional Model for Nematode Thick Filament Core

Henry F. Epstein1, Guan Ying Lu and Philip R. Deitiker2, Irving Ortiz3, Michael F. Schmid2

1 Department of Neurology and the Verna and Marrs McLean Department of Biochemistry, Baylor of Medicine, Houston, Texas
2 The Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, Texas
3 Department of Neurology, Baylor College of Medicine, Houston, Texas

        Understanding the structure and mechanism of assembly of thick
filaments have been long-standing problems in the field of muscle
biology. Cores which represent the backbones of thick filaments and
consist of paramyosin and associated proteins were isolated from the
nematode Caenorhabditis elegans. Electron microscopy of negative stained
and frozen hydrated cores was performed. The resulting images were
analyzed by computing their Fourier transforms, three-dimensional
reconstruction, and by modeling. A preliminary three-dimensional model
is proposed in which the paramyosin constitutes an outer sheath of seven
subfilaments about a set of inner 54-nm-long tubules which repeat every
72 nm. The subfilaments are not closely packed but require cross-linking
by the internal tubules. Each subfilament consist of two strands of
paramyosin molecules which are staggered by 72 nm with respect to one
another. This stagger introduces a 22-nm gap between consecutive
paramyosin molecules in each strand. An offset of the center of the
inner tubules relative to the center of the gap of 6 nm was consistent
with the images and their transforms. This model suggest that the
nonhelical ends of paramyosin and the unpaired gap between adjacent
paramyosin molecules contain sites for the interaction with the inner
tubular proteins. The molecular interactions at this locus would appear
to be critical in the assembly of thick filaments and their regulation.