In the Classroom edited by
Curricular Change Digests
Baird W. Lloyd Miami University Middletown Middletown, OH 45042
Applications of Inorganic Chemistry in Biology An Interdisciplinary Graduate Course
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Nicholas Farrell and Paul Ross Department of Chemistry, Virginia Commonwealth University, 1001 W. Main St., Richmond, VA 23284-2006 Rosette M. Roat Department of Chemistry, Washington College, Chestertown, MD 21620-1197
To emphasize the increasingly interdisciplinary nature of chemistry and to satisfy the broader educational interests of chemistry graduate students, inorganic chemistry professors at Virginia Commonwealth University (VCU) are offering an advanced graduate inorganic chemistry course entitled “Applications of Inorganic Chemistry in Biology”. The course utilizes examples from bioinorganic chemistry to introduce students to advanced topics in synthesis, structural analysis, and analytical methods as practiced by inorganic chemists. Inorganic chemistry professors team-teach the 14-week course, giving a take-home examination at the end of their section. Course discussion topics and a tentative schedule for their presentation are arranged beforehand by the instructors, and this syllabus and the course outline (see Table 1 in JCE Online1 ) are presented to students at the first class meeting. Time constraints prohibit the presentation of many bioinorganic topics and points of view; however, topical interests of the teaching faculty and the students guide the flexible curriculum. The professors found this an eminently workable format, each holding to the topics agreed upon beforehand, but allowing students to suggest new topics or topics for expanded coverage during the latter part of each section of the course. In the iterations described in the full JCE Online article,1 the basic organization of the course covered the following subject areas. 1. Review of coordination geometry of transition metal ions followed by extension of these concepts to distorted geometries seen in most biological metalloproteins. Examples used: plastocyanin, superoxide dismutase, hemocyanin, ascorbate oxidase, cobalamins, myoglobin, hemoglobin, cytochromes. 2. Substitution mechanisms for metals in biological ligand fields and the special circumstances allowing electron transfer through space aided by metal–ligand systems. Examples used: cytochrome oxidase, nitrogenase. 3. Self-assembly in biological systems stressing applications to metal ion–containing systems and catalysis by these super-assemblages. Examples used: iron–sulfur clusters, nitrogenases, cytochrome c oxidase, zinc fingers. 4. Syntheses of models that mimic metal ion–containing biological systems with analysis of their structures and functions using instrumental techniques available to chemists. Examples used: Cu(II) models for blue copper Supplementary materials for this article are available on JCE Online at http://jchemed.chem.wisc.edu/Journal/Issues/1998/ Jun/abs739.html. W
proteins, Ni(III) models for hydrogenase, Mo(V) models for xanthine oxidase. 5. Introduction to medicinal inorganic chemistry. Example used: platinum compounds as anticancer agents.
Two texts were used (1), although students were only required to purchase the Cowan text. Primary sources were used to amplify text materials and stay current with the fast-changing bioinorganic field. The full JCE Online article contains references to 20 texts or books on bioinorganic chemistry, biochemistry, and instrumental analysis and 90 articles surveying the bioinorganic areas covered in the course described.1 Instrumental techniques considered to be unfamiliar to most students, such as electron paramagnetic resonance (EPR), Mössbauer spectroscopy, X-ray absorption spectroscopy, and X-ray crystallography, were explained in somewhat more detail than NMR, IR, or UV–visible techniques where prior knowledge was assumed. Students were referred to standard texts. In general the level of discussion of the instrumental technique was at level appropriate to allow students to understand journal articles that they read. For example, spectroscopic signatures such as the EPR signals for isotropic, axial, and rhombic metal coordination spheres and characteristic Mössbauer isomer shifts for iron–sulfur clusters were used as examples of the utility of these techniques. Many times questions by a student attempting to understand a spectroscopic technique would lead to a more complete discussion of the topic for the entire class. Students were cautioned that synthetic and modeling studies plus use of other analytical techniques such as EPR, NMR, and Mössbauer spectroscopies must confirm X-ray crystallographic interpretations of metalloprotein structure and function. It was emphasized that NMR multidimensional techniques have been used to study complex bioinorganic systems, and results for these solution spectroscopic studies should be compared with the solid-state analyses of X-ray crystallography before conclusions are made on biological structure–function relationships. For example, Hopkins and coworkers (2) have studied a short oligonucleotide duplex interstrand crosslinked to cis-diammineplatinum(II) using high-field NMR analysis, whereas Takahara, Lippard, and coworkers (3) have published the X-ray crystallographic structure of cis-diammineplatinum(II) coordinated to a duplex decamer. Both structural analyses have been welcomed by the community studying the antitumor activity of platinum compounds, and each analysis has engendered lively discussion by workers in the field. Another example is that of the nitro-
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In the Classroom
genase X-ray crystallographic structure first published in 1992 (4 ) and its subsequent modification and correction based on additional EPR information (5–7; see discussion below). In advance of their choosing a particular metalloprotein for intensive study, students were introduced to interpretation of X-ray crystallographic data from the Brookhaven protein database (PDB) and to analysis of ORTEP and stereo diagrams appearing in the primary literature. It was expected that students would be able to interpret these when writing the required term paper for the course. The structure of nitrogenase published by Rees and coworkers (4) was used as an example. It was explained that the original interpretation of the P-cluster having 8 Fe and 8 S atoms with bridging disulfide (5) has been found to be incorrect. Further refinement of the structure has led to the realization that the original crystals studied contained co-crystallized POX (oxidized) and PN (reduced) forms of the protein. Presently the P-cluster pair is believed to have 8 Fe and 7 S atoms, one S atom being four coordinate in the POX form and six coordinate in the PN form (6 ). The importance of understanding EPR and Mössbauer data for the POX and PN forms was pointed out to students (7). Students have as many take home examinations during the term as there are professors teaching (usually two or three). As mentioned above, students choose an interest area by selecting a metalloprotein from a list of those having readily available and downloadable X-ray crystallographic structures. They are assisted in downloading, displaying, and analyzing the appropriate data from the Brookhaven protein database and they are responsible for finding other structure–function information on their chosen metalloprotein. This information is to include analytical methods used to study the metalloprotein and efforts made to model its active site. Students then discuss their findings during class in the latter part of the semester. All team-teaching professors attend the professor-
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led student discussion periods, which are well received by all participants. As their final assignment students report on the protein’s structure and function in a 10–15-page term paper. The paper follows the same pattern of classroom discussion of a bioinorganic system, concentrating on the coordination geometry and nearest-neighbor contacts of the metal-binding site in the protein substrate-binding site and relevance to metalloprotein or enzyme function, mechanism of action of the enzyme or protein, and spectroscopic and model studies on the metal-binding site. The instructors have concluded that their basic goals for the course—introduction to advanced inorganic chemistry topics using bioinorganic examples with emphasis on primary literature sources and computer assisted displays—are being accomplished. Note 1. Supplementary materials for this article are available on JCE Online at http://jchemed.chem.wisc.edu/Journal/Issues/1998/Jun/ abs739.html.
Literature Cited 1. Cowan, J. A. Inorganic Biochemistry: An Introduction, 2nd ed.; WileyVCH: New York, 1996. Lippard, S. J.; Berg, J. Principles of Bioinorganic Chemistry; University Science: Mill Valley, CA, 1994. 2. Huang, H.; Zhu, L;. Reid, B. R.; Drobny, G. P.; Hopkins, P. B. Science 1995, 270, 1842–1845. 3. Takahara, P. M.; Rosenzweig, A. C.; Frederick, C. A.; Lippard, S. J. Nature 1995, 377, 649–652. 4. Rees, D. C.; Kim, J. Nature 1992, 360, 553–560. Georgiades, M. M.; Komiya, H.; Chakrabartie, P.; Woo, D.; Kornuc, J. J.; Rees, D. C. Science 1992, 257, 1653–1659. Kim, J.; Rees, D. C. Science 1992, 257, 1677–1682. 5. Chan, M. K.; Kim, J.; Rees, D. C. Science 1993, 260, 792–794. 6. Peters, J. W.; Stowell, M. H. B.; Soltis, S. M.; Finnegan, M. G.; Johnson, M. K.; Rees, D. C. Biochemistry 1997, 36, 1181–1187. 7. Mouesca, J.-M.; Noodleman, L.; Case, D. A. Inorg. Chem. 1994, 33, 4819–4830.
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