Judith D. Saide, Ph.D.

Associate Professor of Physiology & Biophysics

B.A. Vassar College
Ph. D. Boston University

Phone: (617) 358-8444
Fax: (617) 358-8758
E-mail: jsaide@bu.edu
Address: see below
Link to BU Faculty Profile
Link to ORCID


Fig. Electron micrograph of an isolated Z-disc prepared from honeybee indirect flight muscle. The threadlike structures extending from the surfaces of the Z-disc (observed at the fold) are projectin filaments that link thick myosin containing filaments to the Z-band. Drosophila Z-bands are smaller but structurally similar to those of the honeybee.

Our laboratory studies structural components of the Z-band of striated muscle and other proteins assembled in the contractile apparatus. We use Drosophila indirect flight muscle (Ifm) for our work since the tissue is among the most well ordered in the animal kingdom. The short life cycle of Drosophila is convenient for developmental studies, and the species lends itself to genetic approaches as well.

Using a panel of monoclonal antibodies against components from isolated Drosophila Z-discs, we earlier identified several proteins integrated within the hexagonal Z-band lattice. One of these, projectin, is a large, elastic protein that forms a structural link between thick filaments and the Z-band in Ifm sarcomeres. The protein is analogous to titin in vertebrate skeletal and cardiac muscle and, like titin, has a kinase domain near its C-terminus. Our studies indicate that the protein is oriented with its N-terminus at the Z-band and its C-terminus at the thick filament. Oddly, in Drosophila supercontractile visceral muscle and skeletal muscles, projectin is localized entirely within the A-band. It presumably serves distinct functions in different tissue types.

Zetalin is a 225/245kD protein, also identified by our monoclonal antibodies. The protein is localized within the Z-band lattice, but we currently know nothing about its function. We have so far been unsuccessful cloning the gene encoding this protein. We hope to do so not only to gather sequence information that may suggest its potential functions, but also to examine interactions of this protein (or bacterially expressed zetalin fragments) with other Z-band associated proteins so that we can learn how they are integrated to form a force bearing structure.

Studies on zetalin have uncovered a previously unidentified protein that comigrates with zetalin on SDS gels, but is located within the A-band. By cloning the gene encoding this protein we learned that it derives from the giant stretchin-MLCK gene. We have named the protein stretchin-klp (kettin-like protein) because it has multiple immunoglobulin domains like kettin, another Drosophila Z-band protein. Stretchin-klp migrates as two distinct components (225 and 231 kD). The larger component is myosin dependent and requires the myosin rod (but not the head) to be formed or stabilized. We hope to learn something about this protein’s functions by examining the consequences of its ablation using RNAi approaches.

Related References

Ayme-Southgate A, Saide J, Southgate R, Bounaix C, Cammarato A, Patel S, Wussler C. In indirect flight muscles Drosophila projectin has a short PEVK domain, and its NH(2)-terminus is embedded at the Z-band. J Muscle Res Cell Motil. Feb 8:1-11, 2006

Saide JD (2005) The Insect Z-Band In: Vigoreaux JO, et al. (eds) Nature’s Versatile Engine: Insect Flight Muscle Inside and Out. pp. 150–166. Landes Biosciences, Georgetown, TX. 2006

Patel SR, Saide JD. Stretchin-klp, a novel Drosophila indirect flight muscle protein, has both myosin dependent and independent isoforms. J Muscle Res Cell Motil. Nov 4:1-12, 2005

Cammarato A, Hatch V, Saide J, Craig R, Sparrow JC, Tobacman LS, Lehman W. Drosophila muscle regulation characterized by electron microscopy and three-dimensional reconstruction of thin filament mutants. Biophys JMar;86(3):1618-24, 2004.

Ayme-Southgate, A. Southgate, R., Saide, J. Benian, G.M. Pardue, M.L. Both synchronous and asynchronous muscle isoforms of projectin (the Drosophila bent locus product) contain functional kinase domains. J. Cell Biol. 128(3):393-403, 1995.

Vigoreaux, J.O. Saide, J.D. Valgeirsdottir, K. Pardue, M.L. Flightin, a novel myofibrillar protein of Drosophila stretch-activated muscles. J. Cell Biol. 121(3):587-98, 1993.

Vigoreaux, J.O. Saide, J.D. Pardue, M.L. Structurally different Drosophila striated muscles utilize distinct variants of Z-band-associated proteins. J. Muscle Res. & Cell Motil. 12(4):340-54, 1991.

Saide, J.D. Chin-Bow, S., Hogan-Sheldon, J. Busquets-Turner, L. Z-band proteins in the flight muscle and leg muscle of the honeybee. J. Muscle Res. & Cell Motil. 11(2):125-36, 1990.

Saide, J.D. Chin-Bow, S. Hogan-Sheldon, J. Busquets-Turner, L. Vigoreaux, J.O. Valgeirsdottir, K. Pardue, M.L. Characterization of components of Z-bands in the fibrillar flight muscle of Drosophila melanogaster. J. Cell Biol. 109(5):2157-67, 1989.

Saide, J.D. Identification of a connecting filament protein in insect fibrillar flight muscle. J. Mol. Biol. 153(3):661-79, 1981.

Saide, J.D. Ullrick, W.C. Purification and properties of the isolated honeybee Z-disc. J. Mol. Biol. 87(4):671-83, 1974.

Saide, J.D. Ullrick, W.C. Fine structure of the honeybee Z-disc. J. Mol. Biol. 79(2):329-37, 1973.


Medical Physiology – Course Manager GMS PH 740/MED MS 134

Advanced Human Physiology GMS PH730/731

Endocrinology MED MS128 / GMS PH748

Physiology and Biophysics (Dental) MD514

Contact Us

Judith D. Saide
Department of Physiology & Biophysics
Boston University School of Medicine
700 Albany Street, W408H
Boston MA 02118-2526

Phone: (617) 358-8444
Fax: (617) 358-8758
e-mail: jsaide@bu.edu