Sickle Cell Anemia, a Molecular Disease
Encyclopedia
"Sickle Cell Anemia, a Molecular Disease" is a 1949 scientific paper by Linus Pauling
, Harvey A. Itano, Seymour J. Singer and Ibert C. Wells that established sickle-cell anemia as a genetic disease in which affected individuals have a different form of the metalloprotein
hemoglobin
in their blood. The paper, published in the November 25, 1949 issue of Science
, reports a difference in electrophoretic mobility between hemoglobin from healthy individuals and those with sickle-cell anemia, with those with sickle cell trait
having a mixture of the two types. The paper suggests that the difference in electrophoretic mobility is probably due to a different number of ionizable amino acid
residues in the protein portion of hemoglobin (which was confirmed in 1956 by Vernon Ingram
), and that this change in molecular structure is responsible for the sickling process. It also reports the genetic basis for the disease, consistent with the simultaneous genealogical study by James V. Neel
: those with sickle-cell anemia are homozygous for the disease gene, while heterozygous individuals exhibit the usually asymptomatic condition of sickle cell trait.
The paper introduced the concept of a "molecular disease", and is considered a major impetus to the development of molecular medicine
. The paper helped establish that genes control not just the presence or absence of enzymes (as genetics had shown in the early 1940s) but also the specific structure of protein molecules. It was also an important triumph in the efforts of Pauling and others to apply the instruments and methods of the physical sciences to biology, and Pauling used it promote such research and attract funding.
(a main focal point of Warren Weaver
's efforts to promote what he called "molecular biology" through Rockefeller Foundation
grants). In the mid-1930s, Pauling turned his attention to the physical and chemical nature of hemoglobin. In 1946, he set graduate student Harvey Itano
(who had been previously trained as a physician) the task of finding differences in hemoglobin that might explain sickle cell disease. After failing to find any differences in size, weight, or acid-base titration (despite the advanced instruments available at Caltech), Itano found that oxygen could inhibit the sickling process while various reducing agent
s could speed it up; this was the basis of Pauling and Itano's first publication on the disease. Itano also found that the globin portion of sickle cell hemoglobin had a barely detectable difference in electrical charge.
In order to measure this difference precisely, Pauling assigned graduate student John Singer to work with Itano and another medical researcher, Ibert C. Wells, on using a "Tiselius Apparatus" to perform free-boundary electrophoresis, before leaving in early 1948 for a guest lectureship in England. Using the electrophoresis technique, Pauling's researchers were able to estimate that molecules of sickle-cell hemoglobin had about three more positive charges than normal hemoglobin. They also estimated that blood from those with sickle cell trait was a mixture of 60 percent normal hemoglobin and 40 percent sickle-cell hemoglobin. Near the end of the project, they learned of parallel results by geneticist James V. Neel, who demonstrated the inheritance pattern of the disease by traditional genetic methods; both Neel's work and that of Pauling's group were published in the same issue of Science.
used protein fingerprinting
to show that the key difference between normal hemoglobins and sickle cell hemoglobins was a single difference in one chain of the protein: a glutamic acid
residue in place of a valine
residue.
The molecular disease concept put forward in the 1949 paper also became the basis for Linus Pauling's view of evolution. In the 1960s, by which time it had been shown that sickle cell trait confers resistance to malaria and so the gene had both positive and negative effects and demonstrated heterozygote advantage
, Pauling suggested that molecular diseases were actually the basis of evolutionary change. He also advocated eugenic policies, such as marking all who carry the sickle cell trait and other molecular disease genes, to reduce the number of children born with genetic diseases.
Linus Pauling
Linus Carl Pauling was an American chemist, biochemist, peace activist, author, and educator. He was one of the most influential chemists in history and ranks among the most important scientists of the 20th century...
, Harvey A. Itano, Seymour J. Singer and Ibert C. Wells that established sickle-cell anemia as a genetic disease in which affected individuals have a different form of the metalloprotein
Metalloprotein
Metalloprotein is a generic term for a protein that contains a metal ion cofactor. Metalloproteins have many different functions in cells, such as enzymes, transport and storage proteins, and signal transduction proteins. Indeed, about one quarter to one third of all proteins require metals to...
hemoglobin
Hemoglobin
Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...
in their blood. The paper, published in the November 25, 1949 issue of Science
Science (journal)
Science is the academic journal of the American Association for the Advancement of Science and is one of the world's top scientific journals....
, reports a difference in electrophoretic mobility between hemoglobin from healthy individuals and those with sickle-cell anemia, with those with sickle cell trait
Sickle cell trait
Sickle cell trait describes a condition in which a person has one abnormal allele of the hemoglobin beta gene , but does not display the severe symptoms of sickle cell disease that occur in a person who has two copies of that allele...
having a mixture of the two types. The paper suggests that the difference in electrophoretic mobility is probably due to a different number of ionizable amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
residues in the protein portion of hemoglobin (which was confirmed in 1956 by Vernon Ingram
Vernon Ingram
Vernon M. Ingram, Ph.D., FRS was a German American professor of biology at the Massachusetts Institute of Technology.-Biography:Ingram was born in Breslau, Lower Silesia...
), and that this change in molecular structure is responsible for the sickling process. It also reports the genetic basis for the disease, consistent with the simultaneous genealogical study by James V. Neel
James V. Neel
James Van Gundia Neel was an American geneticist who played a key role in the development of human genetics as a field of research in the United States. He made important contributions to the emergence of genetic epidemiology and pursued an understanding of the influence of environment on genes...
: those with sickle-cell anemia are homozygous for the disease gene, while heterozygous individuals exhibit the usually asymptomatic condition of sickle cell trait.
The paper introduced the concept of a "molecular disease", and is considered a major impetus to the development of molecular medicine
Molecular medicine
Molecular medicine is a broad field, where physical, chemical, biological and medical techniques are used to describe molecular structures and mechanisms, identify fundamental molecular and genetic errors of disease, and to develop molecular interventions to correct them...
. The paper helped establish that genes control not just the presence or absence of enzymes (as genetics had shown in the early 1940s) but also the specific structure of protein molecules. It was also an important triumph in the efforts of Pauling and others to apply the instruments and methods of the physical sciences to biology, and Pauling used it promote such research and attract funding.
Caltech work
Linus Pauling was a prominent physical chemist at the California Institute of TechnologyCalifornia Institute of Technology
The California Institute of Technology is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering...
(a main focal point of Warren Weaver
Warren Weaver
Warren Weaver was an American scientist, mathematician, and science administrator...
's efforts to promote what he called "molecular biology" through Rockefeller Foundation
Rockefeller Foundation
The Rockefeller Foundation is a prominent philanthropic organization and private foundation based at 420 Fifth Avenue, New York City. The preeminent institution established by the six-generation Rockefeller family, it was founded by John D. Rockefeller , along with his son John D. Rockefeller, Jr...
grants). In the mid-1930s, Pauling turned his attention to the physical and chemical nature of hemoglobin. In 1946, he set graduate student Harvey Itano
Harvey Itano
Harvey Akio Itano was an American biochemist best known for his work on the molecular basis of sickle cell anemia and other diseases...
(who had been previously trained as a physician) the task of finding differences in hemoglobin that might explain sickle cell disease. After failing to find any differences in size, weight, or acid-base titration (despite the advanced instruments available at Caltech), Itano found that oxygen could inhibit the sickling process while various reducing agent
Reducing agent
A reducing agent is the element or compound in a reduction-oxidation reaction that donates an electron to another species; however, since the reducer loses an electron we say it is "oxidized"...
s could speed it up; this was the basis of Pauling and Itano's first publication on the disease. Itano also found that the globin portion of sickle cell hemoglobin had a barely detectable difference in electrical charge.
In order to measure this difference precisely, Pauling assigned graduate student John Singer to work with Itano and another medical researcher, Ibert C. Wells, on using a "Tiselius Apparatus" to perform free-boundary electrophoresis, before leaving in early 1948 for a guest lectureship in England. Using the electrophoresis technique, Pauling's researchers were able to estimate that molecules of sickle-cell hemoglobin had about three more positive charges than normal hemoglobin. They also estimated that blood from those with sickle cell trait was a mixture of 60 percent normal hemoglobin and 40 percent sickle-cell hemoglobin. Near the end of the project, they learned of parallel results by geneticist James V. Neel, who demonstrated the inheritance pattern of the disease by traditional genetic methods; both Neel's work and that of Pauling's group were published in the same issue of Science.
Follow-up work
Following the 1949 paper, Itano left the Pauling laboratory to work with Neel; in the following years they used electrophoresis to identify a number of other human hemoglobin variants, including some associated with other diseases. At Caltech, a comparison of the amino acid content of normal and sickle cell hemoglobins showed that they had several differences in chemical makeup, but did not explain the difference in electric charge that made electrophoretic separation possible. The cause of this difference was pinpointed in 1956 and 1957, when Vernon IngramVernon Ingram
Vernon M. Ingram, Ph.D., FRS was a German American professor of biology at the Massachusetts Institute of Technology.-Biography:Ingram was born in Breslau, Lower Silesia...
used protein fingerprinting
Protein fingerprinting
Protein fingerprinting can refer to any of the several methods for identifying or differentiating proteins:*Peptide mass fingerprinting, a method developed in 1993 that uses protein mass spectrometry following SDS-PAGE...
to show that the key difference between normal hemoglobins and sickle cell hemoglobins was a single difference in one chain of the protein: a glutamic acid
Glutamic acid
Glutamic acid is one of the 20 proteinogenic amino acids, and its codons are GAA and GAG. It is a non-essential amino acid. The carboxylate anions and salts of glutamic acid are known as glutamates...
residue in place of a valine
Valine
Valine is an α-amino acid with the chemical formula HO2CCHCH2. L-Valine is one of 20 proteinogenic amino acids. Its codons are GUU, GUC, GUA, and GUG. This essential amino acid is classified as nonpolar...
residue.
The molecular disease concept put forward in the 1949 paper also became the basis for Linus Pauling's view of evolution. In the 1960s, by which time it had been shown that sickle cell trait confers resistance to malaria and so the gene had both positive and negative effects and demonstrated heterozygote advantage
Heterozygote advantage
A heterozygote advantage describes the case in which the heterozygote genotype has a higher relative fitness than either the homozygote dominant or homozygote recessive genotype. The specific case of heterozygote advantage is due to a single locus known as overdominance...
, Pauling suggested that molecular diseases were actually the basis of evolutionary change. He also advocated eugenic policies, such as marking all who carry the sickle cell trait and other molecular disease genes, to reduce the number of children born with genetic diseases.
External links
- It's in the Blood! A Documentary History of Linus Pauling, Hemoglobin and Sickle Cell Anemia — Oregon State University Library
- Sickle Cell Anemia, a Molecular Disease — reproduction of the paper