CHARLOTTESVILLE, VA — Other than condoms and vasectomy, men don’t have any real options for effective contraceptive that they can control. A recent study focused on the tails of sperm may provide insights into changing that.Published online by Developmental Biology, the University of Virginia Health Systems study tells the tale of a new protein discovered within the tails of sperm, and how it might be a perfect target for small-molecule contraceptive drugs.

According to Dr. John Herr, whose team conducted the research, “There’s considerable interest in developing new male contraceptives.”

Herr, who serves as the University’s Center for Research in Contraceptive and Reproductive Health director, explains that his team was searching for proteins that might be key to the reproductive process when it came across the new protein, called a “sperm flagellar energy carrier,” (SFEC).

What makes a SFEC unique is its placement in the process of binding and exchanging energy-carrying molecules inside of a cell. Discovered by researcher Dr. Young-Hwan Kim, SFEC proteins are the fourth in a collection of proteins that perform this service. Its location in this sequence — in the distal part of the tail — has basic scientists, as well as contraceptive drug developers, excited.

As Herr explains it, “One approach to male contraception is to disable sperm from swimming. We think SFEC may be able to play a role in that process.”

A number of things about the SPEC surprised researchers. In addition to its unexpected location, which is unlike three previously identified ATP/ADP carrier proteins, SPEC extensions at both ends of the amino acid sequence were discovered. Such extensions do not exist in other ATP/ADP carriers. It is possible that this is the reason why SPEC proteins can work within the distal sperm tail, in spite of lacking a mitochondria.

“While mitochondria generate energy through an oxidative process,” Kim emphasizes, “recent research indicates that the sperm flagella mainly produces and consumes energy through a process called glycolysis.

This is especially important to the goal of male contraceptive because it is the first time that such an association has been made. “In experiments where glycolysis was blocked,” Kim continues, “the sperm barely quivered, showed no progressive motion, and were infertile.”

When oxidative processes are stopped within a sperm’s mitochondria, the sperm continues to remain active and potent.

Herr foretells that “future male contraceptive drugs will be known as intelligent spermicides,” adding that “at UVa, we’ve coined a great name for this new drug class: spermistatic.”