Seeing the Invisible: 50 Years of Macromolecular Visualization
Brass Models: Placing Atoms into the Electron Density
Before computer graphics became sufficiently efficient, in the late 1970s, brass models were the standard, albeit difficult, way of interpreting the electron density image to construct a detailed atomic model of the protein.
Richardson-lab brass model of Cu,Zn (SOD)
The brass model pieces were designed by Herman Watson & John Kendrew in the late 1960s, to model full atomic coordinates of the high-resolution hemoglobin structures. They are manufactured by Cambridge Repetition Engineers Ltd. This SOD brass model was the first to be built after the structure had been fit on the computer, using the pioneering GRIP75 system at UNC Chapel Hill. The course of the SOD backbone is emphasized by 1/4-inch Tygon tubing, and much finer tubing connects each hydrogen bond, as stabilization for α-helix, β-sheet, and other features. After determining and refining coordinates for the atoms, one can then analyze, interpret, and represent the structure in a variety of ways including ribbon drawings.
Brass model pieces, tools, & supports
On the floor of the case are a few representative peptide and tetrahedral carbon model pieces, connectors, and a wrench for tightening the connector screws. The brass vertical support rods and clamps were blackened for camouflage, by soaking in sodium thiosulfate solution (photographic "fixer", readily available from Dave's darkroom).
Pioneering three-dimensional display technology at UNC graphics lab, ~1977
Crystallographic model-building for macromolecules was then a "driving problem" in computer science for the Computer Graphics Lab at UNC Chapel Hill, headed by Fred Brooks. Their Grip75 was the first successful software/hardware system for fitting a full atomic model into an electron density map, where the computer could constrain accurate local geometry. The Richardsons were the testers during development and the first to use it in practice, for SOD, followed by other visiting crystallographers.
[Britton E, Lipscomb JS, Pique ME, Wright, WV, Brooks FP Jr. The GRIP-75 Man-machine Interface. ACM SIGGRAPH Video Review, (4), (Aug. 1981)]
[Tainer et al. 1982, J. Mol. Biol. 160: 181]