Functional and structural properties of the mitochondrial outer membrane receptor Tom20

Biochemistry. 1998 Sep 22;37(38):13043-51. doi: 10.1021/bi9807456.

Abstract

Tom20 is an outer mitochondrial membrane protein that functions as a component of the import receptor complex for cytoplasmically synthesized mitochondrial precursor proteins. The human homologue, hTom20, consists of an N-terminal membrane anchor region predicted between aa5-25 and a soluble cytosolic domain from aa30 to 145. To analyze the properties of hTom20, we have expressed several truncations of the cytosolic domain as fusion proteins with glutathione S-transferase. Our studies reveal that the cytosolic region of hTom20 is a monomeric protein in solution containing two domains which are involved in different functions of the receptor. The N-terminal region is involved in membrane binding (aa30-60) and recognition of the cleavable matrix targeting signals (aa50-90). In addition, we have demonstrated that the receptor recognizes the alpha-helical state of the matrix targeting signal. The dissociation constant for this interaction in the presence of a detergent which induces this secondary structure is 0.6 microM, one-fifth the value in the absence of detergent. In aqueous solution, the region between aa30 and 60 is loosely folded and stabilized against proteolytic cleavage by interaction with detergents or a matrix targeting signal. Our work further shows that the remainder of the cytosolic domain of hTom20, aa60-145, is a compactly folded globular domain containing a region (aa90-145) that is critical for the recognition of proteins bearing internal signal sequences such as the uncoupling protein and porin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cytosol / metabolism
  • Humans
  • Intracellular Membranes / metabolism*
  • Membrane Proteins / chemistry*
  • Membrane Proteins / genetics
  • Membrane Proteins / physiology
  • Membrane Transport Proteins*
  • Mitochondria / metabolism*
  • Peptide Fragments / chemistry
  • Peptide Fragments / genetics
  • Peptide Fragments / metabolism
  • Protein Binding
  • Protein Folding
  • Protein Sorting Signals / chemistry
  • Protein Sorting Signals / metabolism
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Receptors, Cell Surface*
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Structure-Activity Relationship

Substances

  • Membrane Proteins
  • Membrane Transport Proteins
  • Peptide Fragments
  • Protein Sorting Signals
  • Receptors, Cell Surface
  • Recombinant Proteins
  • TOMM20 protein, human