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X-ray structure of a maquette scaffold
Steve S Huang1, Brian R Gibney, Steven E Stayrook
1The Johnson Research Foundation, Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, 37th and Hamilton Walk, Philadelphia, PA 19102-6059, USA.
Journal of Molecular Biology
|February 19, 2003
Summary
De novo designed protein maquettes, mimicking oxidoreductases, were studied. The crystal structure revealed unexpected anti-parallel four-helix bundle topology, deviating from designed left-handed coiled-coils.
Area of Science:
- Biochemistry
- Structural Biology
- Protein Engineering
Background:
- Maquettes are de novo designed protein scaffolds mimicking natural enzymes like oxidoreductases.
- Four-alpha-helical bundles are common scaffolds, typically exhibiting left-handed coiled-coil structures based on heptad repeats.
Purpose of the Study:
- To determine the X-ray crystal structure of a designed four-helix bundle peptide maquette (L31M).
- To analyze the structural deviations from the intended coiled-coil design and understand factors influencing helix packing.
Main Methods:
- Maquette peptide synthesis and purification.
- X-ray crystallography with MAD phasing to 2.8A resolution.
- Structural analysis of helix-helix interactions and topology.
Main Results:
- The L31M maquette adopted an anti-parallel four-helix bundle structure with "up-up-down-down" topology.
- Unexpectedly shallow inter-helical crossing angles (-5 degrees) were observed, differing from the typical +20 degrees for left-handed coiled-coils.
- No pre-formed heme-binding pocket was present, and deviations were attributed to hydrophobic residue distribution and size.
Conclusions:
- The study highlights that simple heptad repeat patterns are insufficient for reliably designing left-handed coiled-coils.
- The structure of L31M demonstrates that identical helices can pack differently within a bundle, challenging current de novo protein design principles.
- Further refinement of design rules is needed for predictable protein scaffold construction.