The protein content of every living cell is constantly renewed through synthesis of new proteins and degradation of unneeded or misfolded proteins. The only very recently discovered tetrahedral aminopeptidases seem to fulfil a key role in the degradation pathway of bacteria and archaebacteria.
We were able to solve the crystal structure of the tetrahedral aminopeptidase FrvX from the archaeon Pyrococcus horikoshii to 2 Å resolution. FrvX is built of 12 identical subunits forming a symmetric, tetrahedral-shaped 0.5 MDa complex which degrades short peptides to single amino acids. All 12 active sites are located on the inside of the particle in a large central cavity which is connected to the surface by four channels located at the faces of the tetrahedron.

This work was carried out by Santina Russo in the group of Prof. Ulrich Baumann.

References:

• S. Russo, U. Baumann;
  "Crystal Structure of a Dodecameric Tetrahedral-shaped Aminopeptidase"
  J. Biol. Chem., 279, 51275-51281, (2004); doi:10.1074/jbc.M409455200.