Studying the EatA protein passenger domain of enterotoxigenic Escherichia coli (ETEC) bacteria – a cause of disease amongst children in developing countries

My name is Maria Hamunyela, and I am a second year PhD student in the structural biology research group at the University of Pretoria, South Africa. Born and raised in a small town in northern Namibia, I was inspired to pursue my studies in science by women scientists that I have come across. Women in science face extra challenges, having to balance their careers and personal lives. I was raised by strong black women, including my mother, from whom I draw my strength. My parents never had the same opportunities and therefore, on completion of my studies, I will be the first PhD holder in my family.

Although I work for the University of Namibia as a technologist, I chose to continue my studies at the University of Pretoria under the supervision of GCRF START Co-I, Prof Wolf-Dieter Schubert, due to limited research funding and the lack of structural biology facilities in my country. This has provided me with access to world-class equipment, such as the UK’s national synchrotron, Diamond Light Source (Diamond).

Maria Hamunyela is a technologist at the University of Namibia, and a PhD student in the structural biology research group at the University of Pretoria, South Africa. Photo credit: Maria Hamunyela. ©Diamond Light Source

The impact of Escherichia coli (ETEC) and related diseases – the scale of the challenge

I am currently investigating the secreted EatA protein of enterotoxigenic Escherichia coli (ETEC) bacteria. ETEC commonly causes watery diarrhoea in children younger than five years old killing many children in this age group. ETEC also causes malnutrition and stunting in children. I decided to work on this project because ETEC affects young children in developing countries in regions with limited access to clean water and sanitation. This is true of many people in both Namibia and South Africa who are correspondingly severely affected by water and food borne pathogens such as ETEC and Shigella.

Globally, ETEC and Shigella are estimated by the World Health Organisation to cause ~400 million episodes of diarrhoea annually in children under five years of age (WHO 2009) causing moderate and severe stunting in ~2.6 and ~2 million children, respectively[1]. Studying ETEC can help to develop vaccines and drugs against ETEC and related diseases.

Child in a South African village. Photo credit: Rebekka Stredwick. ©Diamond Light Source

Studying the functions and structure of the EatA protein passenger domain

The passenger domain of the EatA protein is required for the virulence of ETEC. It degrades Mucin 2, a protective protein secreted by, and covering the intestinal epithelium. Previous reports show that the EatA passenger domain is a potential vaccine candidate for ETEC and other enteric pathogens such as Shigella flexneri. However, the functional and structural properties of the EatA passenger domain have not been extensively studied. The full biological function of EatA passenger domain is therefore not well understood and might support infections in yet other ways. Studying the functions and the structure of EatA passenger domain will provide a better understanding of ETEC pathogenesis.

A first step in studying the EatA passenger domain will be to introduce an affinity tag in the middle of the protein to simplify protein production and purification. This is non-trivial as both the N- and C-terminal ends are not available for the placement of such a tag and inserting it in the wrong place could affect the stability and the function of the protein. Once the protein has been produced and purified, the substrate specificity will be investigated by designing an enzyme activity assay. Observations on the optimal substrate will ideally allow the development of an inhibitor. Identifying other host proteins that interact with the target protein could provide information about additional functions. Structural and biophysical experiments will include thermal unfolding and refolding studies, co-crystallisation and finally X-ray diffraction to provide a fuller understanding of the role of EatA.

The WHO/UNICEF Integrated Global Action Plan for the Prevention and Control of Pneumonia and Diarrhoea (GAPPD) aims to reduce deaths from diarrhoea in children younger than five to less than 1 per 1000 live births by 2025 (WHO/UNICEF, 2013)[2]. Hopefully designing an inhibitor for EatA will be a fundamental step in achieving this goal

Collaborating with the GCRF START grant and next steps

It took more than a year of searching for opportunities before I came across Prof Wolf-Dieter Schubert and he accepted me to join his structural biology research group at the University of Pretoria. This is how the GCRF START programme afforded me the opportunity to study towards my PhD studies. The main benefit is that I now have access to Diamond, to world-class synchrotron techniques, and I have the reagents that I need to do my research. I am also getting scientific training, not only in the laboratory but through workshops connected to START. In addition, I am fortunate to be a part of a supportive research group.

As I am employed by the University of Namibia as a technologist, I will return to Windhoek (Namibia) in the future, and hopefully start my own academic research group in structural biology. If interesting opportunities arise, I would love to work for an international research facility or even the public sector. While the scientific industry in Namibia is still in its infancy, I may be able to bring my own knowledge to setting up a new company.

Maria Hamunyela is a technologist at the University of Namibia and a PhD student in the structural biology research group at the University of Pretoria, South Africa. Photo credit: Maria Hamunyela. ©Diamond Light Source

Read more about the UN’s Sustainable Development Goals here

[1] accessed 16.03.2021

[2] accessed 16.3.2021