Crystallization and preliminary crystallographic study of carnosinase CN2 from mice

Mammalian tissues contain several histidine-containing dipeptides, of which L-­carnosine is the best characterized and is found in various tissues including the brain and skeletal muscles. However, the mechanism for its biosynthesis and degradation have not yet been fully elucidated. Crystallographic study of carnosinase CN2 from mouse has been undertaken in order to understand its enzymatic mechanism from a structural viewpoint. CN2 was crystallized by the hanging-drop vapour-diffusion technique using PEG 3350 as a precipitant. Crystals were obtained in complex with either Mn²⁺ or Zn²⁺. Both crystals of CN2 belong to the monoclinic space group P2₁ and have almost identical unit-cell parameters (a = 54.41, b = 199.77, c = 55.49 Å, β = 118.52° for the Zn²⁺ complex crystals). Diffraction data were collected to 1.7 and 2.3 Å for Zn²⁺ and Mn²⁺ complex crystals, respectively, using synchrotron radiation. Structure determination is ongoing using the multiple-wavelength anomalous diffraction (MAD) method.