From The National Geographic:
French scientists have identified a protein receptor that resides in the taste buds and may be responsible for sensing fat. As such, this so-called fatty acid transporter, known as CD36, could be to blame for our love of high-fat foods–and could thus serve as a possible target for treatment of obesity. If the link bears out, CD36 would allow fat to join the five previously identified tastes that govern the experience of food: bitter, salty, sweet, sour and “umami,” or savoriness (like the meaty goodness of soup stock).
More here.