Linus Pauling introduced the concept of molecular disease by demonstrating that the gene for sickle cell anemia was directly related to a chemical alteration of hemoglobin in the red blood cells of affected individuals. A few years later, Vernon Ingram identified a single amino acid replacement at position 6 of the beta chains of sickle cell hemoglobin (HbS) and showed that the sequence of the remaining 145 amino acids of the beta chains and all 141 amino acids in the alpha chains of hemoglobin were unchanged compared to normal hemoglobin (HbA). Subsequently, others determined the exact nucleotide substitution mutation in the beta globin gene possessed by sickle cell patients.

These discoveries prompted a stampede of sorts to discover other hemoglobin variants and the corresponding mutations in DNA. There are now on the order of 1000 different mutations known to affect the amino acid sequence or production of hemoglobin. While most of these are single-base-substitution mutations; deletions, insertions, and regulatory mutations are known. The consequences vary from benign to severe, as in the case of thalassemias. Many medical biochemists have made a career studying these usually rare hemoglobinopathies.

Using a list of hemoglobinopathies (alpha-chain, beta-chain, thalassemias), pick an interesting example to investigate as the basis for a 5+ page, double-spaced, well-organized report. Select a variant that no one else in class has selected. Your report should have the following elements:

• A description of the genetic basis of the mutation and its consequences for hemoglobin protein structure, function, and stability. (Append a photocopy of the title page of the original article describing the mutation and/or variant hemoglobin.)
• If your hemoglobin variant involves a change in amino acid sequence, include a computer-generated image of the three-dimensional structure of your hemoglobin highlighting in a different color the location or region of the molecule affected. You can generate this figure using programs available on the Internet. Please generate a figure that is informative.
• Describe any clinical and/or functional effects of the mutation.
• Provide citations to all references and illustrations (if not original) using the standard citation format of the Journal of Biological Chemistry. Part of the purpose of this assignment is for you to demonstrate your ability to find, use, and properly document information from the library. At least five relevant primary references need to be cited.
• If there are other similar or related mutations, they can be integrated into your report.

Suggestion: Because there are many inconsequential hemoglobin variants that are hardly worth writing about, it is important to have a strategy for identifying interesting variants. As with any database search, it is useful to think of clever ways to search to maximize desirable results. Here is a suggestion for a productive strategy. Nobel Prize winner, Max Perutz (1914-2002), spent 20 years working on the X-ray crystallography of hemoglobin before he finally determined its three-dimentional structure in 1957. There after he spent much of the rest of his life studying the structure of interesting hemoglobin variants. One strategy you might try is to search and examine the publications of Max Perutz on PubMed or the Web of Science. Remember, you can often get full text copies through the University of Delaware's electronic journal subscriptions. You may also find some of the sites linked to the course home page of use.