Human Skeletal Muscle Nebulin Sequence Encodes a Blueprint for Thin Filament Architecture
SEQUENCE MOTIFS AND AFFINITY PROFILES OF TANDEM REPEATS AND TERMINAL SH3 (*)
- Kuan Wang(§),
- Marie Knipfer,
- Qi-Quan Huang,
- Ann van Heerden,
- Lillian Chi-Li Hsu,
- Gustavo Gutierrez,
- Xiao-Lan Quian(1) and
- Hansel Stedman(1)
- From the Department of Chemistry and Biochemistry, Biochemical Institute and Cell Research Institute, University of Texas, Austin, Texas 78712
- Department of Surgery, Institute for Human Gene Therapy, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104
- § To whom correspondence should be addressed. Tel. and Fax: 512-471-4065; :kuanw{at}uts.cc.utexas.edu.
Abstract
Analysis of deduced protein sequence and structural motifs of 
5500 residues of human fetal skeletal muscle nebulin reveals the design principles of this giant multifunctional protein in
the sarcomere. The bulk of the sequence is constructed of 
150 tandem copies of 
35-residue modules that can be classified into seven types. The majority of these modules form 20 super-repeats, with each
super-repeat containing a 7-module set (one of each type in the same order). These super-repeats are further divided into
eight segments: with six segments containing adjacent, highly homologous super-repeats, one single repeat segment consisting
of 8 nebulin modules of the same type, and a non-repeat segment terminating with a SH3 domain at the C terminus.
The interactions of actin, tropomyosin, troponin, and calmodulin with nebulin fragments consisting of either repeating modules or the SH3 domain support its role as a giant actin-binding cofilament of the composite thin filament. Such affinity profiles also suggest that nebulin may bind to tropomyosin and troponin to form a composite calcium-linked regulatory complex on the thin filament. The modular construction, super-repeat structure, and segmental organization of nebulin sequence appear to encode thin filament length, periodicity, insertion, and sarcomere proportion in the resting muscle.
Footnotes
-
↵* This work is supported by National Institutes of Health Grant AR43514 and grants from the Foundation for Research (to K. W.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
-
↵1 The abbreviations used are:
- kb
-
kilobase(s)
- bp
-
base pair(s)
- IPTG
-
isopropyl-1-thio-β-D-galactopyranoside
- DTT
-
dithiothreitol.
-
↵2C. L. Shih and K. Wang, manuscript in preparation.
-
- Received May 15, 1995.
- Revision received November 27, 1995.
- © 1996 by The American Society for Biochemistry and Molecular Biology, Inc.
