Donald Caspar, best known for his work determining the structure of the tobacco mosaic virus, died on November 27, 2021 at the age of 94. He is also credited with creating the term “structural biology” to describe the burgeoning field.  

Caspar was born in Ithaca, New York, on January 8, 1927. According to a tribute in Nature by Caspar’s former PhD student Lee Makowski, his father was a chemist and he became interested in topics discussed at home, particularly the first clues about the structure of tobacco mosaic virus (TMV). He earned a physics degree from Cornell University in 1950 and attended Yale University for graduate school, focusing on the structure of TMV for his biophysics thesis.

After obtaining his PhD in 1955, he received a fellowship to King’s College London, where he worked under Rosalind Franklin until the following year. The pair published interrelated papers in Nature describing that the rod-shaped TMV virion was not solid; rather, its proteins were configured into a hollow structure that housed RNA. He also had brief appointments at CalTech, University of Oxford, and Birkbeck College in London.

Moving forward, Caspar’s work tried to reconcile the symmetry of protein subunits in the coats of spherical viruses. In 1962, Caspar and Birkbeck colleague Aaron Klug proposed “quasi-equivalency,” where the units are nearly the same, but slight variations can exist. This idea would later help Caspar explain how plasticity in viral shells occurs. This era is also when Caspar coined the term “structural biology” to better explain the goals of that branch of molecular biology.

In 1958, Caspar opened the Laboratory for Structural Biology within Boston Children’s Hospital. It moved to nearby Brandeis University in 1972 as a joint venture between the hospital and the university, and reflecting the nature of available technology and evolving techniques, was eventually renamed the Brandeis Electron Microscopy Facility.

Caspar left Brandeis as a Professor Emeritus and took a position at the Institute of Molecular Biophysics (IMB) at Florida State University in 1994 at the behest of Makowski, who was then the department’s director. Though he retired as a Professor Emeritus from FSU, he continued to show up daily at the school until the pandemic required him to instead tune into weekly meetings via Zoom. Caspar loved talking to researchers about their work and was a committed mentor, according to Piotr Fajer, current director of IMB, especially to women in the field.

“Don was a feminist, since his early days of working with Rosalind Franklin,” Fajer writes in a tribute, adding that Caspar readily gave women leadership roles in his lab and made sure they were represented at speaking engagements. “Don was always a champion of women scientists.”

In his retirement, his obituary reads, he became an accomplished cook and baker, particularly after his wife became ill.

Caspar was portrayed by Patrick Kennedy in the 2015 production of Photograph 51 on London's West End, which detailed the events surrounding discovering the double helix structure of DNA and the resulting conflict among Rosalind Franklin, James Watson, Francis Crick, and Maurice Wilkins. 

His wife of 50 years, Gwladys, passed away from Alzheimer’s disease in 2011. He is survived by his two children and four grandchildren.