Structural mechanism of SDS-induced enzyme activity of scorpion hemocyanin revealed by electron cryomicroscopy

Structure. 2009 May 13;17(5):749-58. doi: 10.1016/j.str.2009.03.005.


Phenoloxidases (POs) occur in all organisms and are involved in skin and hair coloring in mammals, and initiating melanization in wound healing. Mutation or overexpression of PO can cause albinism or melanoma, respectively. SDS can convert inactive PO and the oxygen carrier hemocyanin (Hc) into enzymatically active PO. Here we present single-particle cryo-EM maps at subnanometer resolution and pseudoatomic models of the 24-oligomeric Hc from scorpion Pandinus imperator in resting and SDS-activated states. Our structural analyses led to a plausible mechanism of Hc enzyme PO activation: upon SDS activation, the intrinsically flexible Hc domain I twists away from domains II and III in each subunit, exposing the entrance to the active site; this movement is stabilized by enhanced interhexamer and interdodecamer interactions, particularly in the central linker subunits. This mechanism could be applicable to other type 3 copper proteins, as the active site is highly conserved.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Binding Sites
  • Catalytic Domain
  • Cryoelectron Microscopy
  • Enzyme Activation
  • Hemocyanins / chemistry*
  • Hemocyanins / metabolism
  • Models, Molecular
  • Monophenol Monooxygenase / chemistry*
  • Monophenol Monooxygenase / metabolism*
  • Protein Conformation
  • Protein Subunits / chemistry
  • Protein Subunits / metabolism
  • Scorpions / metabolism*
  • Sodium Dodecyl Sulfate / pharmacology*
  • Surface-Active Agents / pharmacology*


  • Protein Subunits
  • Surface-Active Agents
  • Sodium Dodecyl Sulfate
  • Hemocyanins
  • Monophenol Monooxygenase

Associated data

  • PDB/3IXV
  • PDB/3IXW