Bacteria probably aren't alone in using MDR pumps
it is likely that there are probably many as yet unidentified such
proteins lurking in membranes of all kinds of cells, says Sikic. The latest
estimates say 2,000 of the approximately 100,000 human genes are included
in the family of proteins to which the MDR pump also belongs, says Sikic.
Only a fraction of those genes and the proteins they encode have been studied,
While scientists expect to discover many more MDR-like proteins, they
all are puzzled by the broad spectrum of chemicals, called substrates, that
the pumps repel. The list of such substrates includes a surprisingly wide
variety of compounds, from naturally occurring substances such as alkaloids
in plants and antibiotics in dirt, to man-made chemicals such as dyes and
some pesticides. Scientists have found only one common thread: all the substances
repelled by MDR pumps are relatively hydrophobic (they don't dissolve easily
Scientists are consequently coming to believe that there are likely a
variety of pumps, each dealing with a group of its own, similar substrates.
But researchers such as Lewis also suspect that an as yet unidentified natural
chemical substrate has kept the pumps around throughout evolution.
Meanwhile, researchers around the globe continue to search by land and
by sea for the MDR signature: indeed, bottom-dwelling flounder are among
the most recent club members. As scientists better understand how and why
cells universally use MDR pumps, they may well be able to beat nature at
its own game.