Spontaneous formation of L-isoaspartate and gain of function in fibronectin

J Biol Chem. 2006 Nov 24;281(47):36466-76. doi: 10.1074/jbc.M604812200. Epub 2006 Oct 2.

Abstract

Isoaspartate formation in extracellular matrix proteins, by aspartate isomerization or asparagine deamidation, is generally viewed as a degradation reaction occurring in vivo during tissue aging. For instance, non-enzymatic isoaspartate formation at RGD-integrin binding sites causes loss of cell adhesion sites, which in turn can be enzymatically "repaired" to RGD by protein-l-isoAsp-O-methyltransferase. We show here that isoaspartate formation is also a mechanism for extracellular matrix activation. In particular, we show that deamidation of Asn263 at the Asn-Gly-Arg (NGR) site in fibronectin N-terminal region generates an alpha(v)beta3-integrin binding site containing the L-isoDGR sequence, which is enzymatically "deactivated" to DGR by protein-L-isoAsp-O-methyltransferase. Furthermore, rapid NGR-to-isoDGR sequence transition in fibronectin fragments generates alpha(v)beta3 antagonists (named "isonectins") that competitively bind RGD binding sites and inhibit endothelial cell adhesion, proliferation, and tumor growth. Time-dependent generation of isoDGR may represent a sort of molecular clock for activating latent integrin binding sites in proteins.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Binding, Competitive
  • Cell Adhesion
  • Extracellular Matrix / metabolism
  • Fibronectins / chemistry*
  • Humans
  • Integrins / chemistry
  • Isoaspartic Acid / chemistry
  • Isoaspartic Acid / physiology*
  • Melanoma, Experimental
  • Mice
  • Models, Molecular
  • Molecular Sequence Data
  • Oligopeptides / chemistry
  • Recombinant Proteins / chemistry

Substances

  • Fibronectins
  • Integrins
  • Isoaspartic Acid
  • Oligopeptides
  • Recombinant Proteins
  • arginyl-glycyl-aspartic acid