This year we're thankful for our grantee Prof. Zeilstra-Ryalls and her team, who finished their work co-supported by the RGHGF in 2024. We're ecstatic to share a final interview with the Professor spanning from her inspiration to become a researcher to the summary of her findings in cutting-edge cancer research.
1. Can you tell us a bit about you and your professional background? Why did you choose gene regulation and protein structure-function relationships as your field of research?
I studied biology as an undergraduate because, like many undergrads, I didn't know of many other career options so thought I would become an MD – to help people. One summer during my undergraduate years, I was able to get some firsthand experience in medicine by completing a program to become a nurse's assistant. I came to realize that I was not comfortable interacting with people in the manner that delivering health care requires, to put it euphemistically, and I decided I no longer wanted to pursue a medical career. So, what then?
I was fortunate that the biology curriculum for the Bachelor of Science degree at Florida Atlantic University included courses in genetics and biochemistry, both of which opened up my thinking about science and what research is. After graduating, I moved to the Netherlands where I studied molecular sciences at Wageningen University. During that time, as part of the degree program, I was required to complete a "practical period" at a different institution. As a US citizen, it was reasonable for me to do this in a lab in the US, and it was arranged that I would work for 6 months in the lab of Professor Ronald Somerville at Purdue University.
After I earned my "ingeniuer" (engineer) degree from Wageningen, and with the encouragement of Prof. Somerville, I decided to apply to PhD programs in the US. I was offered a graduate fellowship at the University of Michigan in the Human Genetics Program, but I was also offered a fellowship in the Biochemistry Program at Purdue. It was a difficult decision for me, but I chose to go to Purdue.
I joined Somerville's lab, where I worked on a protein in Escherichia coli called the Trp repressor. This is a DNA binding protein, and it functions to regulate genes that code for the enzymes required for biosynthesis of the amino acid tryptophan in that organism. At that time, a relatively small number of protein structures had been determined. But the ability to crystallize the protein and its importance as a regulator attracted the attention of workers in the field, and the crystal structure was solved while I was still a PhD student at Purdue. I was amazed, and astounded by what it revealed. As shown below, the two polypeptides of the dimeric protein are hooked around each other!
We learn in our beginning biology courses that polypeptides are made by ribosomes using a process called translation. But what events transpire that can make possible this spectacular intertwined protein?
This image is from RCSB PDB (RCSB.org), which is the US data center for the Protein Data Bank. It is an open access digital data resource for 3 dimensional protein structures. The accession number for the image is 1TRO, and it is the crystal structure of the Trp repressor protein bound to its target DNA sequence. The two polypeptides of the protein are colored in blue and purple, the two chains of the DNA are brown and green. In order for the protein to bind to DNA, it must be complexed with the amino acid tryptophan (shown in grey).
Close to the time I was graduating from Purdue, molecular chaperones were discovered. These are essential proteins that help mediate the proper folding and assembly of other proteins. I wanted to find out how Trp repressor and other proteins achieved their proper folded configurations, and I thought learning about chaperones would be the way to do that. I joined Professor Costa Georgopoulos' lab at the University of Utah to study chaperones, where I focused on those proteins. I learned that, as is so often true of research, far from answering questions about how proteins achieve their final active structures, it ended up raising even more questions: We know these chaperone proteins are necessary, but what are
the mechanistic details as to how they carry out their function?
After three years, I started in the lab of Professor Samuel Kaplan at the University of Texas Health Sciences Center in Houston to study how a bacterium (called Rhodobacter sphaeroides at the time, but since renamed Cereibacter sphaeroides) could switch from obtaining cellular energy by aerobic respiration (like animals) to obtaining cellular energy by photosynthesis (like plants). This seemed to me to be the perfect set-up to return to studying gene regulation – how did these bacteria sense and respond to environmental cues in order to deploy the molecular machinery to perform the appropriate energy metabolism? That is, how do they "know" to turn on genes for aerobic respiration and turn off genes for
photosynthesis in the presence of oxygen, but turn off genes for aerobic respiration and turn on genes for photosynthesis in the absence of oxygen? And what about responding to the availability of light?
I came to realize that the study of the biosynthesis of a family of compounds called tetrapyrroles provided the means to address this question. Tetrapyrroles include heme (the oxygen-carrying component of red blood cells, and also a key element of respiration) and also chlorophyll (the indispensable compound for photosynthesis). So, I thought that learning how genes coding for the enzymes that catalyze tetrapyrrole formation are regulated would connect me to the regulatory processes used by the bacteria in detecting
and responding to oxygen and light. I focused on the first step in tetrapyrrole biosynthesis, because it was already known that this was a highly regulated event. It had also been discovered that C. sphaeroides has two genes coding for enzymes that catalyze this step, which afforded me the opportunity to pursue both my interest in gene regulation as well as protein structure-function relationships.
I worked in the lab of Sam Kaplan for 4 years, and then succeeded in obtaining a faculty position as an assistant professor at Oakland University where I was tenured and promoted to associate professor. I subsequently moved to Bowling Green State University as a full professor. I researched genes and enzymes involved in tetrapyrrole biosynthesis and their regulation ever since. In writing this, I am surprised to see that my path seems to have been straightforward. It seems that pursuing one's curiosity ends up clearing the way.
"In writing this, I am surprised to see that my path seems to have been straightforward. It seems that pursuing one's curiosity ends up clearing the way."
3. Please tell us a little bit about the wonderful research you conducted using the
RGHGF Grant (what you can share publicly)?
During my studies of tetrapyrrole biosynthesis, I came to learn about photodynamic therapy. This involves the application of a substance called 5-aminolevulinic acid (ALA), which is used by C. sphaeroides and human cells to make heme. A precursor to heme is protophorphyrin IX (PPIX), and this molecule can absorb light to become energized. In the presence of oxygen, the energized PPIX results in the production of harmful reactive species of oxygen. Thus, the therapy protocol subsequent to the application of ALA is to expose the cells to light, which results in cell death due to the production of the reactive oxygen species. A limitation in the effective use of photodynamic therapy to treat tumors is the targeted delivery of ALA to the tumors, and especially to within the tumor.
The goal of this project was to design and engineer bacteria that produce and secrete ALA for the purpose of using them to deliver the ALA to, and within the tumor. Importantly, the bacteria are non-pathogenic, unlike many others currently being investigated, or under development for similar cancer therapies.
4. You are well known for your passion to empower and teach students skills for real-world research. Why is this so important to you?
I have had many excellent mentors over the years. Ron Somerville, my PhD advisor, was exceptional. I aspire to be as good as he was – it's been an aspiration that I don't think I have achieved as I know that I fall short with respect to the patience he had! So, one reason it is important is my own sense of "paying it forward". But I also have come to know that a student's research experience can alter their entire academic perspective – they find, possibly for the first time, that they can actually use what they are learning.
They also find out what research is really like, that it is incremental and that it takes a lot of
intense thinking and hard work – but that success generates an incredible sense of accomplishment and self-satisfaction. It is only through direct experience that an understanding of this is possible.
An additional reason is that learning how to do science takes a long time, and it is important students undertake the first steps sooner rather than later. Finally, I think that there are benefits for all students, including students who do not pursue research as a career. They learn that they don't need to just accept anything they see or hear as fact. Rather, they, as do all of us, have the means and ability to find sources and primary data so that they can make their own assessments and reach their own conclusions.
"I also have come to know that a student's research experience can alter their entire academic perspective – they find, possibly for the first time, that they can actually use what they are learning."
5. What do you plan to do now that the grant for this project is completed?
The work on this project was part of an overall plan. I have, and will continue work on developing bacterial-mediated cancer therapy. I have developed a strong collaboration with Professor Masako Harada at Michigan State University, and we have already applied for additional funding to support the next step in the process. The outcomes from this project comprised the preliminary results for that proposal. I also have other projects I am working on, such as investigating the toxicity mechanisms of the so-called "forever chemicals", PFAS. I am continuing my studies of protein structure-function relationships and gene regulation as well.
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