Scientists from Caltech have solved the crystal structure of an ATP-binding Cassette (ABC) transporter called HI1470/1 from the bacteria Haemophilus influenzae. This particular transporter, which is a member of a large family of related proteins prevalent in most organisms including humans, is responsible for moving nutrients across cell membranes. The structure of HI1470/1 exhibits an alternate conformation to that previously observed for the related transporter BtuCD, such that their pathways for moving nutrients open to opposite sides of the membrane. These results give scientists a look at both the beginning and ending stages of how proteins transport nutrients across the membrane bilayers that surround all cells.

Using x-ray diffraction data from SSRL beam line 9-2, subtle distinctions were found in the HI1470/1 transporter that could be relevant to the function of the protein. Namely, a twist of about 9 degrees was found about an axis perpendicular to the translocation pathway when central internal structures are aligned. These differences may shed light on how the protein changes from inward to outward shapes during the process of transporting nutrients.

Though the findings are not immediately applicable, they may prove important in future medicinal uses. For instance, some members of the ABC transporter family are involved in multi-drug resistance. Understanding the mechanism through which substances are transported across cell membranes may be the first step in developing inhibitors to keep medicines inside cells, which would increase a drug's effectiveness. Also, antibiotics could be developed that inhibit the transporters in infectious bacteria, starving them of essential nutrients.

To learn more about this research see the full scientific highlight at:
http://www-ssrl.slac.stanford.edu/research/highlights_archive/abc_rees07.html

H.W. Pinkett, A. T. Lee, P. Lum, K. P. Locher, D. C. Rees. (2007) An Inward-Facing Conformation of a Putative Metal-Chelate-Type ABC Transporter. Science 315, 373 - 377.