Andrew David McLachlan. 25 January 1935—8 July 2022

Andrew McLachlan enjoyed a wide-ranging career, starting as a theoretical chemist and ending as a molecular biologist. After reading physics as an undergraduate at Trinity College, Cambridge, he joined the Theoretical Chemistry Section of the Chemistry Department to study for a PhD. His work on electron spin resonance then led to his election as a research fellow at Trinity. Following postdoctoral work in the United States, he returned to Cambridge as a college lecturer in physics at Trinity and was eventually appointed a university lecturer in chemistry. Despite a productive research programme in various aspects of theoretical chemistry, he decided that a move into the newly developing subject of molecular biology would provide an exciting opportunity. Accordingly, in 1967 he accepted an offer to join the Medical Research Council Laboratory of Molecular Biology. The initial plan was to work on the mechanism of oxygen uptake by haemoglobin, but he quickly became interested in wider problems of protein structure. In particular, he developed methods for aligning the sequences of different proteins and for detecting repeated sequences and motifs, leading to an interest in the evolution of protein sequences. In collaboration with others, he applied his methods to a wide range of proteins, providing important understanding of their structures and relationships.