Discipline: Chemistry and Chemical Sciences
Subcategory: Biochemistry (not Cell and Molecular Biology and Genetics)
Room: Park Tower 8209
Viridiana E. Herrera - University of Oklahoma
Co-Author(s): Samantha M. Powell, University of Oklahoma, Norman OK; Jun Yi, University of Oklahoma, Norman OK ; Bing Wang, University of Oklahoma, Norman OK ; Leonard M. Thomas, University of Oklahoma, Norman OK; George B. Richter-Addo, University of Oklahoma, Norman OK
Mammals require dioxygen (O2) for respiration. The blood protein, hemoglobin (Hb), carries O2 from the lungs to the muscle protein, myoglobin (Mb), where O2 is stored for later use. These proteins use a heme cofactor to achieve their function; embedded within the heme group is an iron (Fe) atom that directly binds O2. Organic nitrosoalkanes (RNO) are valence isoelectronic with O2, this feature gives RNOs high affinities towards hemoproteins such as Mb and Hb. As a result, RNOs often compete with O2 in the binding pocket to form ?inhibitory? Fe(II)-RNO complexes.
Several biologically relevant organic compounds such as drugs and antibiotics contain amine (RNH2), and/or nitro (RNO2) functional groups. Under normal or perturbed physiological conditions (e.g., during infection), nitrosoalkanes can results from the oxidative metabolism of amines or by the reduction of nitro containing compounds. In human hemoglobin, binding of certain RNOs to the heme site may lead to methemoglobinemia or hemolytic anemia, which can then cause detrimental heme loss and successive Fe accumulation in the spleen. In human liver cytochrome P450, RNOs inhibit the same protein responsible for detoxification of xenobiotics.
Although the issues described above pose serious health hazards, there is little information regarding the mode of binding of RNOs to Mb and Hb, and the architectural consequences of such binding to protein structure and function. This research is designed to investigate the interaction of Mb and Hb with nitrosoalkanes of increasing sizes, to determine the effects of ligand sterics on RNO binding and the resulting stability of the complexes. We also designed experiments to elucidate the importance of distal pocket composition on ligand coordination and reactivity by incorporating the distal pocket mutant H64A into our research.
This study has resulted in multiple high-resolution X-ray crystal structures that show the interactions between different nitrosoalkanes with Mb and Hb in 3-dimensional space. These structures show that nitrosoalkanes, regardless of their size, bind directly to iron, thereby competing with O2. Surprisingly, in Mb, our smallest nitrosoalkane occupies a pocket below the heme that has been identified as a site for additional O2 storage. Altogether, these structures illustrate how RNOs, which are naturally occurring metabolites of drugs and foreign compounds, bind Mb and Hb disturbing the vital roles these proteins have on O2 respiration. Our resulting X-ray crystal structures and reactivity trends, as determined by UV-vis spectroscopy, will be presented and discussed in detail.
Funder Acknowledgement(s): Price Family Foundation Institute of Structural Biology, Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK ; National Science Foundation (Grants CHE-1213674 and CHE-1566509 to GBR-A); Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health under grant number P20GM103640.
Faculty Advisor: George B. Richter-Addo, firstname.lastname@example.org
Role: Protein purification, crystallization, X-ray data collection, and structure refinements were performed by me, as well as reactivity trends as determined by UV-vis spectroscopy. This work was performed by me with supervision and guidance from our senior graduate student Samantha Powell, and former group members Dr. Bing Wang and Dr. Jun Yi. The final crystal structures were verified by Dr. Leonard M. Thomas.