W0147

Despite the fact that many cultures around the world value and utilize garlic as a fundamental component of their cuisine as well as of their medicine cabinets, relatively little is known about the plant’s protein configuration that is responsible for the specific properties of garlic. Here, we report the three-dimensional structure of the garlic enzyme alliinase at 1.5 Å resolution. Alliinase constitutes the major protein component in garlic bulbs, and it is able to cleave carbon-sulfur bonds. The active enzyme is a pyridoxal-5'-phosphate-(PLP)-dependent homodimeric glycoprotein and belongs to the class I family of PLP-dependent enzymes. In addition, it contains a novel epidermal growth factor-(EGF)-like domain that makes it unique among all PLP-dependent enzymes.

Each subunit of the homodimer is comprised of three domains: the N-terminal domain with the EGF-like structure, the central PLP-binding domain and the C-terminal domain. The PLP-cofactor is bound via a Schiff base to Lys 251.

Based on the structure, a reaction mechanism can be proposed, which opens the door to a more rational understanding of garlic sulfur chemistry, and it may even provide the basis for the design of altered selectivities and therefore altered therapeutic features of garlic and other Allium plants.