A missing link in cupredoxins: Crystal structure of cucumber stellacyanin at 1.6 Å resolution

P. John Hart, Aram M. Nersissian, Reinhold G. Herrmann, Robert M. Nalbandyan, Joan Selverstone Valentine, David Eisenberg

Research output: Contribution to journalArticlepeer-review

161 Scopus citations


Stellacyanins are blue (type I) copper glycoproteins that differ from other members of the cupredoxin family in their spectroscopic and electron transfer properties. Until now, stellacyanins have eluded structure determination. Here we report the three-dimensional crystal structure of the 109 amino acid, non-glycosylated copper binding domain of recombinant cucumber stellacyanin refined to 1.6 Å resolution. The crystallographic R- value for all 18,488 reflections (σ > 0) between 50-1.6 Å is 0.195. The overall fold is organized in two β-sheets, both with four β-strands. Two α-helices are found in loop regions between β-strands. The β-sheets form a β-sandwich similar to those found in other cupredoxins, but some features differ from proteins such as plastocyanin and azurin in that the β-barrel is more flattened, there is an extra N-terminal α-helix, and the copper binding site is much more solvent accessible. The presence of a disulfide bond at the copper binding end of the protein confirms that cucumber stellacyanin has a phytocyanin-like fold. The ligands to copper are two histidines, one cysteine, and one glutamine, the latter replacing the methionine typically found in mononuclear blue copper proteins. The Cu-Gln bond is one of the shortest axial ligand bond distances observed to date in structurally characterized type I copper proteins. The characteristic spectroscopic properties and electron transfer reactivity of stellacyanin, which differ significantly from those of other well-characterized cupredoxins, can be explained by its more exposed copper site, its distinctive amino acid ligand composition, and its nearly tetrahedral ligand geometry. Surface features on the cucumber stellacyanin molecule that could be involved in interactions with putative redox partners are discussed.

Original languageEnglish (US)
Pages (from-to)2175-2183
Number of pages9
JournalProtein Science
Issue number11
StatePublished - Nov 1996
Externally publishedYes


  • X-ray crystallography
  • azurin
  • cucumber basic protein
  • cupredoxins
  • glutamine copper ligand
  • phytocyanins
  • plastocyanin
  • stellacyanin

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology


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