first molecular model of enzyme bovine carboxypeptidase A (CPA)
Date: circa 1968
Inventory Number: 2000-1-0025
Classification: Molecular Model
Subject:
Maker: William Nunn Lipscomb Jr. (born 1919)
User: Wolcott Gibbs Memorial Laboratory, Harvard University (1911 - 2000)
Cultural Region:
Place of Origin:
Dimensions:
202.8 x 125 x 110 cm (79 13/16 x 49 3/16 x 43 5/16 in.)
estimated weight: 225 lb. (102.1 kg)
Description:
Hand-braised copper with chemical bonds in plastic of colors yellow, white, red, and light blue. Yellow areas contain pairs of small cylinders, one of which is labeled with an amino acid abbreviation, the other with a number. Some areas are painted colors, including fluorescent green, fluorescent orange, white, and red, and contain styrofoam spheres.
FunctionThis molecular model depicts the enzyme Bovine Carboxypeptidase A (CPA). CPA was the first enzyme to be represented with a detailed three-dimensional model based on X-ray crystallographic data alone.
During the late 1960s, William Lipscomb became interested in demonstrating the high resolution of structural detail that could be achieved using this technique. This complex biological molecule was chosen for analysis due to its relatively low molecular weight (34,600) and the ease with which it may be crystallized.
CPA is made up of 307 amino acid residues, some of which are labeled and numbered above. Each one of these amino acids was positioned in space based on the identification of its unique shape in electron density maps produced from the X-ray crystallographic data. These electron density maps were hand-drawn on large plastic sheets overlayed on computer printout showing where to draw the lines. The modelers then hung the plastic sheets in stacks in front of a light source and taped small plastic chips onto the sheets where they deduced atoms to be. Next, the 3-D position of each plastic chip was measured. Finally, this model was constructed with the atoms of the brass model at these 3-D positions, building amino acids to the vertical struts of the model frame, or to the growing polypeptide chain. To turn the two-dimensional electron density data into a three-dimensional model for complex molecules such as CPA took weeks of work.
This enzyme, secreted by the pancreas to assist in digestive processes, requires a zinc ion to function, which is represented here by the white sphere.
During the late 1960s, William Lipscomb became interested in demonstrating the high resolution of structural detail that could be achieved using this technique. This complex biological molecule was chosen for analysis due to its relatively low molecular weight (34,600) and the ease with which it may be crystallized.
CPA is made up of 307 amino acid residues, some of which are labeled and numbered above. Each one of these amino acids was positioned in space based on the identification of its unique shape in electron density maps produced from the X-ray crystallographic data. These electron density maps were hand-drawn on large plastic sheets overlayed on computer printout showing where to draw the lines. The modelers then hung the plastic sheets in stacks in front of a light source and taped small plastic chips onto the sheets where they deduced atoms to be. Next, the 3-D position of each plastic chip was measured. Finally, this model was constructed with the atoms of the brass model at these 3-D positions, building amino acids to the vertical struts of the model frame, or to the growing polypeptide chain. To turn the two-dimensional electron density data into a three-dimensional model for complex molecules such as CPA took weeks of work.
This enzyme, secreted by the pancreas to assist in digestive processes, requires a zinc ion to function, which is represented here by the white sphere.
Historical AttributesMade by Professor William Nunn Lipscomb, Jr., currently Abbott and James Lawrence Professor of Chemistry, Emeritus, and his students at Wolcott Gibbs Memorial Laboratory.
ProvenanceTransferred to CHSI in 2000 from the Department of Chemistry arranged by Dr. Alan Kingsley Long, Director of the Laboratories of the Department of Chemistry and Earth and Planetary Sciences.