4jb8
From Proteopedia
Caspase-7 in Complex with DARPin C7_16
Structural highlights
FunctionCASP7_HUMAN Involved in the activation cascade of caspases responsible for apoptosis execution. Cleaves and activates sterol regulatory element binding proteins (SREBPs). Proteolytically cleaves poly(ADP-ribose) polymerase (PARP) at a '216-Asp-|-Gly-217' bond. Overexpression promotes programmed cell death. Publication Abstract from PubMedDesigned ankyrin repeat proteins (DARPins) are well-established binding molecules based on a highly stable nonantibody scaffold. Building on 13 crystal structures of DARPin-target complexes and stability measurements of DARPin mutants, we have generated a new DARPin library containing an extended randomized surface. To counteract the enrichment of unspecific hydrophobic binders during selections against difficult targets containing hydrophobic surfaces such as membrane proteins, the frequency of apolar residues at diversified positions was drastically reduced and substituted by an increased number of tyrosines. Ribosome display selections against two human caspases and membrane transporter AcrB yielded highly enriched pools of unique and strong DARPin binders which were mainly monomeric. We noted a prominent enrichment of tryptophan residues during binder selections. A crystal structure of a representative of this library in complex with caspase-7 visualizes the key roles of both tryptophans and tyrosines in providing target contacts. These aromatic and polar side chains thus substitute the apolar residues valine, leucine, isoleucine, methionine, and phenylalanine of the original DARPins. Our work describes biophysical and structural analyses required to extend existing binder scaffolds and simplifies an existing protocol for the assembly of highly diverse synthetic binder libraries. Design, construction, and characterization of a second-generation DARPin library with reduced hydrophobicity.,Seeger MA, Zbinden R, Flutsch A, Gutte PG, Engeler S, Roschitzki-Voser H, Grutter MG Protein Sci. 2013 Jul 19. doi: 10.1002/pro.2312. PMID:23868333[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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