Conformation change of hornet silk proteins in the solid phase in response to external stimulation

Abstract

Hornet silks adopt a variety of morphology such as fibers, sponge, films, and gels depending on the preparation methods. We have studied the conformation change of hornet silk proteins (Vespa mandarina) as regenerated films, using chiroptical spectrophotometer universal chiroptical spectrophotometer 1, which can measure true circular dichroism spectra without artifact signals that are intrinsic to solid-state samples. The spectra showed that the proteins in films alter the conformation rapidly from the α-helix to the coiled coil and then to a β-sheet structure in response to heat/moisture treatment, but the transformation stopped at the coiled coil state when the sample was soaked in EtOH/water solution. Water is required for the α-helix to the coiled coil transition, and extra energy is required for the further transition to a β-sheet structure. This is the first successful circular dichroism study of fibril silk proteins to follow the conformation changes in the solid state. This work shows that proteins can undergo conformational changes easily even in the solid phase in response to external stimuli, and this can be traced by solid-phase-feasible chiroptical spectrophotometers. Application of unnatural stress to proteins gives valuable insights into their structure and characteristics.

Fast and artifact‐free circular dichroism measurement of solid‐state structural changes

“…34 Thus, UCS-1-3 spectrophotometers can reveal dynamic aspects of structural changes in the solid and condensed phases for organic, inorganic, and biological samples that could not be achieved with commercially available CD spectrophotometer. 1,2,[4][5][6][7][8][10][11][12][13]34 However, although UCSs are very powerful for chirality measurements in the solid state, extra time and effort involving sophisticated sets of procedures as described above are necessary to obtain true chirality signals. Since our first development of solid-state applicable spectrophotometers based on the StokesÀMueller matrix method in 2001, excellent work on Mueller Matrix Polarimetry has been reporteed.…”

“…Using UCS‐1, we have obtained valuable information on structural changes in the solid state. The examples include (a) detection of the decreasing CD intensity and eventually the sign inversion of the 3 A 2g → 3 T 1g (P) Ni (II) d–d transition of α‐Ni(H 2 O) 6 ・SO 4 single crystals observed on lowering temperature, which is not accompanied by obvious X‐ray structural changes 10 ; (b) facile conformation changes of hornet silk protein in films on exposure to steam for 5 s 11 ; (c) the gradual development of chiral aggregates of zinc porphyrins in a KBr matrix upon interaction with a droplet of chiral 1‐cyclohexylethylamine 12 ; and many others 13–33 …”

“…Using DRCD, the rearrangement of molecules in powdered crystals on sublimation of one component, benzoquinone, has been successfully followed 34 . Thus, UCS‐1–3 spectrophotometers can reveal dynamic aspects of structural changes in the solid and condensed phases for organic, inorganic, and biological samples that could not be achieved with commercially available CD spectrophotometer 1,2,4–8,10–13,34 . However, although UCSs are very powerful for chirality measurements in the solid state, extra time and effort involving sophisticated sets of procedures as described above are necessary to obtain true chirality signals.…”