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Identification of a matrix-binding domain in MAGP1 and MAGP2 and intracellular localization of alternative splice

Fernando Segade1, Barbara Crippes Trask, Thomas J Broekelmann

  • 1Department of Cell Biology and Physiology and the Division of Pulmonary and Critical Care Medicine, Barnes-Jewish Hospital and Washington University School of Medicine, St. Louis, Missouri 63110, USA.

The Journal of Biological Chemistry
|January 18, 2002
PubMed

Insights

Researchers identified a specific matrix-binding domain in MAGP1 essential for extracellular matrix (ECM) targeting. This domain, containing 7 cysteines, dictates MAGP1’s ECM association, revealing insights into microfibril interactions.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Extracellular Matrix Research

Background:

  • Microfibrils, key components of the extracellular matrix (ECM), are crucial for tissue structure and function.
  • Microfibril-associated glycoprotein 1 (MAGP1) is a protein known to associate with microfibrils.
  • The precise molecular mechanisms governing MAGP1's interaction with the ECM remain incompletely understood.

Purpose of the Study:

  • To elucidate the molecular basis of MAGP1's interaction with other microfibrillar proteins.
  • To identify the specific region within MAGP1 responsible for its targeting to the ECM.
  • To investigate the role of cysteine residues and splice variants in MAGP1's ECM association and function.

Main Methods:

  • Expression of MAGP1 deletion constructs in a mammalian cell system to model microfibril assembly.
  • Site-directed mutagenesis to assess the importance of specific amino acid residues, particularly cysteines.
  • Analysis of MAGP1 splice variants (MAGP1B, MAGP1D) using chimeric proteins with green fluorescent protein (GFP) in rat lung fibroblasts.

Main Results:

  • A 54-amino acid sequence in the carboxyl-terminal region of MAGP1 was identified as a matrix-binding domain sufficient for ECM targeting.
  • The binding activity of this domain is critically dependent on the presence of 7 cysteine residues.
  • MAGP2, despite sequence similarity, failed ECM association due to a single amino acid change.
  • Human-specific (MAGP1B) and mouse-specific (MAGP1D) splice variants localized intracellularly, suggesting alternative functions.

Conclusions:

  • The carboxyl-terminal 54-amino acid sequence constitutes a functional matrix-binding domain for MAGP1, mediated by 7 cysteine residues.
  • Specific amino acid substitutions can disrupt ECM binding, as exemplified by MAGP2.
  • Intracellular localization of MAGP1 splice variants suggests a potential second functional site for MAGP1 beyond the ECM.

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