Molecular Characteristics and Interactions of the Intermediate Filament Protein Synemin

doi:10.1074/jbc.274.41.29493

Molecular Characteristics and Interactions of the Intermediate Filament Protein Synemin

INTERACTIONS WITH α-ACTININ MAY ANCHOR SYNEMIN-CONTAINING HETEROFILAMENTS*

From the Muscle Biology Group, Departments of Biochemistry, Biophysics, and Molecular Biology and of Animal Science, Iowa State University, Ames, Iowa 50011-3260 and the ^§Department of Cell Biology, Neurobiology, and Anatomy, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267

Abstract

Synemin is a cytoskeletal protein originally identified as an intermediate filament (IF)-associated protein because of its colocalization and copurification with the IF proteins desmin and vimentin in muscle cells. Our sequencing studies have shown that synemin is an unusually large member (1,604 residues, 182,187 Da) of the IF protein superfamily, with the majority of the molecule consisting of a long C-terminal tail domain. Molecular interaction studies demonstrate that purified synemin interacts with desmin, the major IF protein in mature muscle cells, and with α-actinin, an integral myofibrillar Z-line protein. Furthermore, expressed synemin rod and tail domains interact, respectively, with desmin and α-actinin. Analysis of endogenous protein expression in SW13 clonal lines reveals that synemin is coexpressed and colocalized with vimentin IFs in SW13.C1 vim+ cells but is absent in SW13.C2 vim− cells. Transfection studies indicate that synemin requires the presence of another IF protein, such as vimentin, in order to assemble into IFs. Taken in toto, our results suggest synemin functions as a component of heteropolymeric IFs and plays an important cytoskeletal cross-linking role by linking these IFs to other components of the cytoskeleton. Synemin in striated muscle cells may enable these heterofilaments to help link Z-lines of adjacent myofibrils and, thereby, play an important role in cytoskeletal integrity.

Footnotes

↵* This research was supported in part by grants from the United States Dept. of Agriculture, NRICGP Award 96-35206-3744, Muscular Dystrophy Association, and American Heart Association, Heartland Affiliate. This is Journal Paper J-18253 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA 50011, Projects 3444, 3349 and 2127, and supported by Hatch Act and State of Iowa funds.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) .
↵‡ Present address: Dept. of Cell Biology and Biochemistry, Astra Hässle AB, S-431 83, Mölndal, Sweden.
↵¶ To whom correspondence should be addressed: Muscle Biology Group, 3110 Molecular Biology Bldg., Iowa State University, Ames, IA 50011-3260. Tel: 515-294-5036; Fax: 515-294-0453; E-mail: rmrobson@iastate.edu.
↵2 M. M. Bilak and R. M. Robson, unpublished observations.
↵3 S. W. Sernett and R. M. Robson, unpublished observations.
↵4 T. W. Huiatt, D. J. Graves, and R. M. Robson, unpublished observations.
Abbreviations:

IF

intermediate filament

BSA

bovine serum albumin

ECL

enhanced chemiluminescence

kb

kilobase(s)

mAb

monoclonal antibody

pAb

polyclonal antibody

PAGE

polyacrylamide gel electrophoresis

UTR

untranslated region
- Received June 14, 1999.
- Revision received July 30, 1999.
The American Society for Biochemistry and Molecular Biology, Inc.