To commemorate the award of an Honorary Fellowship to Professor Sir John E Walker, FRS, FMedSci, Nobel Laureate in Chemistry, on 6 February 2019 Professor Sir John delivered The Cambridge Philosophical Society's Honorary Fellows Lecture.
Lecture Title: "The fuel of life"
This lecture was devoted to how the biological world supplies itself with energy, and what medical consequences ensue when the energy supply chain in our bodies is damaged or defective, and how we can put our knowledge of how ATP is made to benefit mankind. We derive our energy from sunlight, via photosynthesis in green plants, providing high energy components in the foods that we eat. We harvest that energy by “burning” (oxidising) the high energy components, releasing cellular energy in a controlled way to generate the fuel of life, in the form of the molecule adenosine triphosphate (or ATP for short). The key steps in this process take place in the mitochondria inside the cells that make up our tissues. They serve as biological “power stations” containing millions of tiny molecular turbines, the ATP synthase, that rotate like man-made turbines, churning out the cellular fuel in large quantities, which is then delivered to all parts of our bodies to provide the energy to make them function. Each of us makes and expends about 60 kg of this fuel every day of our lives. The ATP synthases consist of two rotary motors linked by a stator and a flexible rotor. Rotation of the membrane bound rotor is driven by the proton motive force, itself generated by oxidative metabolism (or by photosynthesis in green plants). A unique direction of rotation ensures that ATP is made from ADP and phosphate in the globular catalytic domain. However, during anoxia, ATP made by glycolysis serves as the source of energy and is hydrolysed in the catalytic domain. Then the rotor turns in the opposite sense and protons are pumped outwards through the membrane domain, and away from the catalytic domain. However, for reasons yet to be uncovered some eubacterial ATP synthases, which in many respects resemble the ATP synthases in metazoans, are unable to carry out this hydrolytic reaction.
Why this is so, is of great practical interest today, as the ATP synthase in Mycobacterium tuberculosis is a validated drug target for the treatment of tuberculosis. In 2011, 1.4 million people died from tuberculosis, and Mycobacterium tuberculosis is now the second greatest killer of mankind by a single infectious agent, surpassed only by HIV /AIDS. A further 7.3 million have been diagnosed with the active form of the disease, and a third of the world’s population, currently 7.2 billion people, has been estimated to have a latent TB infection, and to be at risk of progressing to the active disease. Today, multi-drug resistant tuberculosis, extensively drug-resistant tuberculosis, and totally resistant tuberculosis add to the difficulties of treating the disease. In 2015, multidrug-resistant TB strains of M. tuberculosis caused an estimated 480,000 new cases of TB and 250,000 deaths. The differences between human ATP synthases and those in bacterial pathogens can be exploited in the fight against bacterial resistance to antibiotics.
The origins and propagation of life on earth depended upon developing an ability to generate ATP, and so the lecture ended by discussing the question about how such a complex machine was put together early in evolution. Clues are to found in the process of how the modern ATP synthase is assembled.