Crystallographic studies of transport proteins and ligands

The transport of particles, whether electrons, small molecules or macromolecules, is essential to life as we know it. All forms of life use the transport of particles to gain energy for growth and reproduction and to move the building blocks of life from their place of internalization or synthesis to their ultimate destination. Understanding the means of transport is essential to understanding the mechanisms of life.; Crystallographic studies were undertaken to elucidate the structures of several transport proteins in order to understand their role in the life of their parent organisms. These included a blue copper protein, rusticyanin, involved in the electron transfer chain in a bacterium, Thiobacillus ferrooxidans, the hemoglobin from the domestic house cat, Felis sylvestris catus, with an arsenical moiety attached, and the hemoglobin molecule from the North American opossum, Didelphis virginiana .; The structure determination of rusticyanin was undertaken to understand the role of the ligands to the copper atom in determining the reduction potential of the molecule. The structure was determined using multiplewavelength anomalous dispersion (MAD) to solve the phase problem. The final structure showed that there was no clear answer to the question of the role of the copper ligands in the reduction potential. However it did show that the overall structure, while similar to other blue copper proteins, had some significant differences which could be interpreted in light of the extreme acid stability of rusticyanin.; The structure of hemoglobin from cats, while similar to that of other animals, is fairly unique in its ability to bind to arsenicals. It is of interest to determine this binding motif in order to gain insight into the method of binding of arsenicals to proteins. Arsenicals have a long history of use as drugs and poisons and a possible future role as a therapeutic agent in the treatment of cancer. An understanding of the method of interaction of arsenic and proteins will enable researchers to design more optimum arsenic compounds with increased efficacy and reduced side effects.; A successful molecular replacement solution was determined using the program X-PLOR, however the final structure has yet to be determined.; Opossum hemoglobin is unique in that it has a glutamine substituted for the distal histidine in the alpha subunit. It is the only mammalian hemoglobin known which does not have two histidines coordinating the heme iron atom; this is a lethal mutation in humans. The role of the distal histidine in hemoglobins is uncertain, the structure of opossum hemoglobin will help us to understand it.; The molecular replacement search for opossum hemoglobin was accomplished using X-PLOR and the refinement of the structure is in progress.