In Memoriam: Don Caspar

December 1, 2021

MSA has the sad duty to report the passing of Dr. Don Caspar on November 27. This is a great loss of one of the pioneers of structural biology. Born in 1927, he was an Emeritus Faculty Member at Florida State University. The Caspar and Klug quasi-equivalence theory of icosahedral virus construction (Caspar DL, Klug A. 1962. Physical principles in the construction of regular viruses. Cold Spring Harbor Symposia on Quantitative Biology. 27: 1–24) was based on the recognition that structural proteins are adaptable molecules that can self-assemble by bonding together in different ways within a highly ordered structure (Aaron Klug won the 1982 Nobel Prize in Chemistry for his work on virus structure). The original concept was based mainly on electron microscope studies, and has now been refined to take account of the atomic resolution structure of viruses, and other details of protein–protein interactions. Quasi-equivalence continues to be an important component of the philosophical basis for how we think about macromolecular assemblies. Dr. Caspar was a long-time friend and colleague of Aaron Klug as well as many of the early pioneers in molecular biology, including Rosalind Franklin.