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The heavy-light chain loop of human cathepsin-L modulates its activity and stability

Michael Fairhead1, Christopher F van der Walle

  • 1Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 27 Taylor Street, Glasgow, G4 0NR, UK.

Protein and Peptide Letters
|January 29, 2008
PubMed

Insights

Investigating human cathepsin-L function revealed that a specific loop (residues 286-289) indirectly impacts enzyme activity. Modifying this loop affects protease activity and conformational stability, but not substrate affinity.

Area of Science:

  • Biochemistry
  • Enzymology
  • Structural Biology

Background:

  • Human cathepsin-L is a key protease with structural similarities to shrimp cathepsin-L and silicatein-alpha.
  • Sequence alignment highlights potential functional roles for specific loop regions.

Purpose of the Study:

  • To investigate the functional significance of the heavy to light chain loop (residues 286-289) in human cathepsin-L.
  • To determine the impact of loop modifications on enzyme activity, substrate affinity, and conformational stability.

Main Methods:

  • Site-directed mutagenesis to delete or substitute the heavy to light chain loop.
  • Enzyme activity assays to measure specific protease activity.
  • Determination of kinetic parameters (Km).
  • Analysis of protein conformational stability.

Main Results:

  • Deletion of the loop (E 286 to E 289) decreased protease activity by 81%.
  • Deletion of adjacent residues (S 290 to N 293) decreased activity by 63%.
  • Substitution with a silicatein-alpha loop decreased activity by 35%, with largely unchanged Km values.
  • Loop deletion did not alter procathepsin-L stability, while adjacent residue deletion increased it.

Conclusions:

  • The heavy to light chain loop (E 286 to E 289) indirectly influences human cathepsin-L activity.
  • Modifications to this loop affect enzyme activity through conformational changes, not altered substrate affinity.
  • These findings provide insights into cathepsin-L structure-function relationships.

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