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Frances Arnold

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Frances Hamilton Arnold is a distinguished American chemical engineer and a Nobel Laureate. She currently serves as the Linus Pauling Professor of Chemical Engineering, Bioengineering, and Biochemistry at the California Institute of Technology, also known as Caltech. In 2018, she received the Nobel Prize in Chemistry for her pioneering work in directed evolution. This method allows scientists to engineer enzymes, which are biochemical molecules that catalyze, or speed up, chemical reactions. Her work bridges the gap between molecular biology and industrial application, creating tools for a more sustainable future.

Directed evolution is the central mechanism of Arnold's research. In nature, evolution by natural selection changes proteins over very long periods through random mutations. Arnold accelerated this process by using an iterative strategy of mutagenesis and screening. First, she introduces specific mutations into the underlying sequences of proteins. Next, she tests these mutations to see if they improve a desired function. If a mutation is successful, she uses that improved protein as the starting point for the next round. This cycle of mutation and selection allows for the optimization of molecules for specific, often human-made, tasks.

Arnold's method can create many different types of biological systems. She has used directed evolution to create improved enzymes and entire metabolic pathways. She has also engineered genetic regulatory circuits and whole organisms. One notable application involves creating enzymes that function in extreme environments. While natural enzymes usually work within a narrow temperature range, Arnold's engineered enzymes can function at both very high and very low temperatures. She has even evolved enzymes to perform entirely new chemical reactions, such as cyclopropanation, for which no specific natural enzyme previously existed.

Arnold's journey to scientific leadership was marked by significant independence. She grew up in the Pittsburgh area and graduated from Taylor Allderdice High School in 1974. During her teenage years, she lived independently and worked various jobs, including as a cab driver. Despite some academic challenges during this period, she achieved near-perfect scores on standardized tests. She attended Princeton University, where she earned a Bachelor of Science in mechanical and aerospace engineering in 1979. After working as an engineer in South Korea and Brazil, she earned a PhD in chemical engineering from UC Berkeley in 1985.

One of her most significant early successes occurred in 1993. In a seminal study, she used directed evolution to engineer a version of the enzyme subtilisin E. She wanted this enzyme to remain active in an organic solvent called DMF, which is a highly unnatural environment for most proteins. She used error-prone PCR, a method to induce mutations, through four sequential rounds of mutagenesis. After each round, she screened the bacteria to see which ones could hydrolyze the milk protein casein in the presence of DMF. By the end of the process, she discovered an enzyme with 256 times more activity in DMF than the original version.

Beyond the laboratory, Arnold has made a massive impact on industry and policy. She is a co-inventor on more than 40 US patents and has co-founded several companies. These include Gevo, Inc., which focuses on renewable resources, and Provivi, which researches alternatives to pesticides. In 2019, she joined the board of directors for Alphabet Inc., the parent company of Google. Since 2021, she has served as an external co-chair of the President's Council of Advisors on Science and Technology (PCAST). In this role, she works to integrate scientific expertise into government policymaking.

Her research continues to address global challenges in energy and agriculture. At Caltech, her laboratory studies how directed evolution can lead to environmentally friendly chemical synthesis. This includes developing enzymes that convert renewable biomass into fuels and chemicals. For example, she evolved bacteria to produce isobutanol, a precursor for many important substances and renewable fuels. By engineering these biological pathways, she helps create a bridge between the natural world and the complex needs of modern technology.

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