LAUSR

Ken Holmes was a versatile experimentalist. He applied his knowledge of the physical sciences to developing methods for determining the structure of biological samples. The need for more intense X-rays for the fiber diffraction of an insect muscle led to his outstanding contribution to structural biology: the use of synchrotron radiation as a source of X-rays for determining biological structures. This revolutionized protein crystallography, resulting in the determination of the structure of hundreds of thousands of proteins. Ken was also a good communicator. Many will remember his enthusiastic descriptions of “How muscle works,” even if they were not the definitive solution. Ken read physics at St John’s College, Cambridge, obtaining a BA in 1955. He then moved to Birkbeck College in London, where he worked with Rosalind Franklin and later with Aaron Klug on the structure of the tobacco mosaic virus (TMV). TMV was known to be rod-shaped with protein subunits arranged helically around the long axis of the rod; there was also an RNA component. Ken and Franklin obtained X-ray fiber diagrams of oriented gels of the virus in a capillary using a finely focused X-ray camera. Diffraction patterns from samples with a single mercury atom on each protein subunit enabled them to determine the symmetry parameters of TMV (Franklin and Holmes, 1956, 1958). The isomorphous replacement method also revealed that a single strand of RNA is inside the virus and that there is central hollow core. Ken received a PhD for this work in 1959. The technique of X-ray fiber diffraction learnt from Franklin was to influence Ken’s future career. In 1960, Ken moved to the Children’s Hospital in Boston to continue the work on TMV with a post-doctoral position in Don Caspar’s lab. Ken perfected the preparation of virus particles, and the large amounts of data were processed on an early IBMmachine (Caspar and Holmes, 1969). Carolyn Cohen was also at the Children’s Hospital working on the structure of muscle proteins. The anterior byssus retractor muscle (ABRM) ofMytilus edulis was particularly interesting because it went into a “catch” state to keep the two halves of the shell shut. Ken was able to squeeze the ABRM into a capillary, with a technique similar to the one he used with TMV, forming an oriented gel. This gave very good X-ray fiber diffraction patterns, which Ken and Cohen showed were consistent with a coiled coil α-helical structure in paramyosin in the core of the myosin filaments (Cohen and Holmes, 1963). Although this introduction to muscle research was a sideline, it became the chief interest for most of Ken’s career. Back in England in 1962, Kenmoved to the Laboratory of Molecular Biology (LMB) in Cambridge to continue work on TMV in Aaron Klug’s group. During his early years at LMB, Ken developed a rotating anode X-ray generator with Bill Longley in order to improve the fine focus needed for the TMVwork. This was a prototype of the Elliott X-ray generator. Meanwhile, John Pringle had become Linacre Professor of Zoology in Oxford in 1961. He was interested in the mechanism of oscillatory contraction of insect flight muscle. Richard Tregear joined him and set out to measure changes in the X-ray fiber diagram during the cyclical contraction of the flight muscle. Pringle had introduced the giant water bug, Lethocerus, as a model system for work on the flight muscle. Themuscle fibers are up to 1 cm long, easily separated, and ideal for mechanical measurements. Tregear visited Cambridge to get advice from Ken about setting up an Elliott rotating anode in Oxford. He brought the flight muscle from the largest Lethocerus species, Lethocerus maximus. They used the Holmes-Longley fine focus rotating anode X-ray generator and an X-ray camera with a gold-plated glass mirror and bent quartz crystal monochromator (developed by Ken and Hugh Huxley) to take low-angle pictures of fibers in rigor and fibers relaxed by adding adenosine 5’-triphosphate (ATP) to the solution. There Edited by: Adrian Goldman, University of Helsinki, Finland