Structure-function studies of an engineered scaffold protein derived from Stefin A. II: Development and applications of the SQT variant

Protein Eng Des Sel. 2011 Sep;24(9):751-63. doi: 10.1093/protein/gzr019. Epub 2011 May 25.


Constrained binding peptides (peptide aptamers) may serve as tools to explore protein conformations and disrupt protein-protein interactions. The quality of the protein scaffold, by which the binding peptide is constrained and presented, is of crucial importance. SQT (Stefin A Quadruple Mutant-Tracy) is our most recent development in the Stefin A-derived scaffold series. Stefin A naturally uses three surfaces to interact with its targets. SQT tolerates peptide insertions at all three positions. Peptide aptamers in the SQT scaffold can be expressed in bacterial, yeast and human cells, and displayed as a fusion to truncated pIII on phage. Peptides that bind to CDK2 can show improved binding in protein microarrays when presented by the SQT scaffold. Yeast two-hybrid libraries have been screened for binders to the POZ domain of BCL-6 and to a peptide derived from PBP2', specific to methicillin-resistant Staphylococcus aureus. Presentation of the Noxa BH3 helix by SQT allows specific interaction with Mcl-1 in human cells. Together, our results show that Stefin A-derived scaffolds, including SQT, can be used for a variety of applications in cellular and molecular biology. We will henceforth refer to Stefin A-derived engineered proteins as Scannins.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Aptamers, Peptide / chemistry*
  • Aptamers, Peptide / genetics
  • Aptamers, Peptide / metabolism*
  • Cell Line, Tumor
  • Circular Dichroism
  • Cyclin-Dependent Kinase 2 / chemistry
  • Cyclin-Dependent Kinase 2 / genetics
  • Cystatin A / chemistry*
  • Cystatin A / genetics
  • Cystatin A / metabolism*
  • Humans
  • Molecular Sequence Data
  • Mutation
  • Protein Array Analysis
  • Protein Engineering / methods*
  • Proto-Oncogene Proteins c-bcl-2 / chemistry
  • Proto-Oncogene Proteins c-bcl-2 / genetics
  • Sequence Alignment
  • Structure-Activity Relationship
  • Two-Hybrid System Techniques


  • Aptamers, Peptide
  • Cystatin A
  • PMAIP1 protein, human
  • Proto-Oncogene Proteins c-bcl-2
  • CDK2 protein, human
  • Cyclin-Dependent Kinase 2