Structural Studies of Echinococcus granulosus Fatty-acid-binding Protein 1 and Human Semicarbazide-sensitive Amine Oxidase

Abstract: The parasite Echinococcus granulosus causes hydatid disease, a major zoonosis. A fatty-acid-binding protein, EgFABP1, is important for the parasite, as it must acquire almost all its lipids from its environment or the host. The structure of EgFABP1 has been solved and refined to 1.6 Å resolution. The structure reveals that EgFABP1 has the 10-stranded β-barrel fold typical of the family of intracellular lipid-binding proteins. Human semicarbazide-sensitive amine oxidase (SSAO; EC 1.4.3.6), also known as vascular adhesion protein-1, is a copper-containing monoamine oxidase that occurs both as a membrane-bound protein and in a soluble form in plasma. SSAO has been implicated in glucose transport in adipocytes, the differentiation of adipose cells and the leukocyte extravasation process. Toxic reaction products have been suggested to cause some of the vascular complications associated with diabetes and SSAO is therefore of pharmaceutical interest.The structure of a truncated, soluble form of human SSAO has been determined to 2.5 Å resolution. The structure reveals that a leucine residue located adjacent to the active site could function as a gate controlling its accessibility. An RGD motif is displayed on the surface where it could be involved in integrin binding and possibly play a role in the shedding of SSAO from the membrane. Carbohydrate moieties are observed at five out of six potential N-glycosylation sites. Carbohydrates attached to Asn 232 flank the active site entrance and might influence substrate specificity. The structure also reveals a vicinal disulfide bridge, which we hypothesise could act as a redox switch involved in the protein’s mechanism of action. The structure of a complex of SSAO and the irreversible inhibitor 2-hydrazinopyridine has been solved and refined to 2.9 Å resolution. Both structures together will aid efforts to identify natural substrates, provide valuable information for the design of specific inhibitors and direct further studies.