On April 25, 2024, our close friend, colleague and mentor, Professor Stuart Ferguson sadly passed away. We had the privilege of working with Stuart as doctoral students, post-doctoral researchers and research collaborators. Stuart was an inspiration to us and hundreds of other students and researchers throughout his career. Stuart took a ‘problem-based’ approach to research. Not for Stuart was the handle-turning, churning out of ‘omics’ data of every kind to then try to make a story out of it. No, Stuart liked a problem to solve and then conceived imaginative experiments with which to solve it – and then he told a story, and there were some great ones! Stuart was also a great educationalist, inspiring students in tutorials and co-writing, with David Nichols, three editions of a text book on bioenergetics that is still being used as the go-to text for university courses throughout the world.
Stuart’s academic life began as a student of chemistry at Merton College, Oxford. He then undertook his DPhil in Oxford under the supervision of George Radda FRS during which he studied the enzyme ATP synthase and the bioenergetics in mitochondria. Through elegant chemical modification experiments, he was one of the first to identify the ATP/ADP-binding site co-operativity of ATP synthase. During his post-doctoral work in Oxford in the mid-1970s, Stuart began to work on the bioenergetics of Paracoccus denitrificans, a close prokaryotic relative of mitochondria. Working with Douglas Kell and Philip John he carried out important experiments probing membrane potential and ΔpH in submitochondrial particles and Paracoccus membrane vesicles.
In 1978, Stuart moved to the University of Birmingham to take up a lectureship in the Department of Biochemistry and develop his own independent research group. He continued to advance his work on the bioenergetics of Paracoccus denitrificans, embracing studies on the ATP synthase, methylotrophy, c-type cytochromes and, perhaps most notably, denitrification. In Gram-negative bacteria, many of the proteins carrying out these processes are located in the periplasm. Stuart championed the periplasm as a metabolically active sub-cellular compartment and rejected the widely used term ‘periplasmic space’.
While at Birmingham, Stuart shared a research laboratory with the late Baz Jackson, who was working on the bioenergetics of photosynthetic bacteria. Together, they formed a formidable partnership in bacterial bioenergetics that developed a global reputation. One area they developed together was anaerobic photo-respiration in photosynthetic bacteria, working with Alastair McEwan to establish a new role for anaerobic respiration in redox poising of the photosynthetic electron transport system.
In 1985, Stuart moved back to Oxford, accepting the William R. Miller Tutorial Fellowship at St. Edmund Hall. In 1994, he was appointed to an ad hominem Readership, and three years later, he received the title of Professor of Biochemistry. He continued to work with Baz Jackson on redox balancing, which provided the opportunity for one of us (Richardson) to join the two of them as a doctoral student. We both then had the pleasure of working together with Stuart in Oxford as a doctoral student (Berks) and a post-doctoral researcher (Richardson). Over the next 40 years in Oxford, Stuart made a huge contribution to the global understanding of the biochemistry of denitrification, the process by which nitrate is sequentially reduced via nitrite, nitric oxide and nitrous oxide to dinitrogen. Bacteria can use this process to sustain growth and catabolism in the absence of oxygen. Stuart characterised many of the enzymes involved in denitrification and explored how they were organised across the cytoplasmic membrane to enable energy conservation (generation of a protonmotive force). He established how some of the substrates were transported across the membrane and how cofactors involved in electron transfer were synthesised and incorporated into the mature proteins.
Stuart demonstrated that the cytotoxic nitric oxide was a free intermediate in denitrification and was among the first to identify a specific enzyme that detoxified it – the nitric oxide reductase. Particularly notable was the structural characterisation, with James Moir and Vilmos Fülöp, of the hemoprotein cytochrome cd1 nitrite reductase that converts nitrite into nitric oxide. All this carried out before nitric oxide became Science journal’s molecule of the year in 1992! The potent greenhouse gas nitrous oxide is also a free intermediate in denitrification. We now know that denitrifying bacteria are a major agricultural source of this environmentally damaging gas, but Stuart was one of the first to identify and characterise the enzyme that can destroy it by converting it to the more inert dinitrogen gas.
While his primary focus was always Paracoccus, Stuart’s work had widespread significance and occasionally led him to work on organisms he had never expected to. In his own words Stuart describes, in an interview with FEBS Letters, an example of how his work took him into trypanosomes: ‘We are interested in how the bacterial electron transport proteins from denitrifying bacteria work and how they are synthesized and post-translationally modified. We use a wide range of tools to study these problems such as mutagenesis, protein expression and in vitro reconstitution. Additionally, it turns out there are at least three ways to post-translationally modify a group of these proteins, the c-type cytochromes, depending on whether we talk about a human or plant mitochondria, an E. coli cell or a plant thylakoid. In addition, a post-doc in our lab, James Allen, recently noticed that there is no sign of the typical post-translational apparatus in trypanosomes, which cause sleeping sickness, so it looks like there is a fourth way to do it. I never thought we would be interested in trypanosomes but our research has taken a new direction.’
Stuart had a great sense of humour and was wonderful story-teller (if prone to just a little bit on exaggeration!). It was an amazing experience to share our academic and social lives with him, and most of all, to have Stuart as one of our closest friends. He leaves us with a strong legacy, captured in over 250 publications, and he was awarded the Keilin Medal by the UK Biochemical Society in 2001. He is remembered fondly by many friends and colleagues. He is also remembered as a wonderful husband and father by Tina, Robin and George.
