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BMMB Graduate Program

Nathan Soulier named Honorable Mention for 2020 Richard L. and Norma L. McCarl Graduate Scholarship.

Image of Nathan Soulier

Nathan Soulier, a graduate student in his seventh year in the BMMB Program, has earned Honorable Mention for both the 2020 Robert T. Simpson Award for Innovative (“Risky”) Research and the 2020 Richard L. and Norma L. McCarl Graduate Scholarship. Both awards were accompanied by $500.00 cash prizes.

The Graduate Student Award for Innovative (Risky) Science was created by the family of Robert T. Simpson in 2005 in memory of the former professor of biochemistry and molecular biology who embraced the concept of high-risk, high-impact research. The award was established to recognize an individual graduate student, working under the direction of a biochemistry and molecular biology faculty member, who has made important and innovative contributions in forwarding their research in their specific area of study.

The Richard L. and Norma L. McCarl Graduate Scholarship recognizes the contributions of Richard L. McCarl, and the support of his wife, Norma.  Richard L. McCarl earned his Ph.D. in Agricultural and Biological Chemistry from Penn State in 1961.  He was asked to remain at Penn State, where he served with distinction as a faculty member within the Department of Biochemistry.

Soulier received honorable mention recognition for his research showing how cyanobacteria use far-red light to perform oxygen-evolving photosynthesis, performed under the guidance of Ernest C. Pollard Professor in Biotechnology and Professor of Biochemistry and Molecular Biology, Donald Bryant. The Bryant Laboratory has demonstrated that some terrestrial cyanobacteria extensively remodel their photosynthetic apparatus by synthesizing new chlorophylls, phycobiliproteins, and reaction centers in far-red light. These studies have shown how these organisms can grow at the bottom of dense microbial mats or the shade of plants.



Grpahic detailing the research being conducted by Nathan Soulier
The relationship between chromophore planarity (i.e., "flatness") and phycobiliprotein absorbance. Panels a and c show a side and top view, respectively, of the phycocyanobilin chromophores bound by the indicated phycobiliprotein subunits, either ApcB1, CpcA1, ApcA1, ApcD1, or ApcD4. Panel c shows the ring-planes extrapolated from each pyrrole ring of the chromophores and the angles between them, which indicate how planar the chromophore is in the protein environment. All the models with the exception of the ApcD4 phycocyanobilin are from structures deposited in the Protein Data Bank. No structure exists for a far-red phycobiliprotein, but this study presents evidence supporting the hypothesis that a more planar chromophore in the alpha subunit is primarily responsible for far-red light-absorbance in phycobiliproteins. 

The primary focus of Soulier’s research has been to demonstrate the mechanisms by which some cyanobacteria adapt to perform photosynthesis in different colors (wavelengths) of light. More specifically, Soulier has investigated the structural differences in red and far-red light-absorbing forms of allophycocyanin, an intensely colored cyanobacterial phycobiliprotein that exhibits far-red fluorescence with a high quantum yield.

Scientists have yet to be successful in obtaining structural information regarding far-red light-absorbing allophycocyanin through crystallography. Because of this, Soulier decided to approach his research differently and address the issue by using homology modeling and point/region-specific mutants to both eliminate or to bestow far-red absorbance on allophycocyanin. He believed this approach would provide structural insights into the basis for far-red-light absorbance within these proteins.

Allophycocyanin is typically a red-light-absorbing protein (~650 nanometers) that forms the core of the main light-harvesting complex in cyanobacteria, the phycobilisome. However, in certain light conditions some cyanobacteria express alternative forms of allophycocyanin that harvesting far-red light ~700-750 nanometers) instead of red light. These allophycocyanins are essential in allowing such organisms to perform photosynthesis with light wavelengths not used by plants, algae, and most other cyanobacteria.

Soulier’s research has provided detailed information on the structual differences that lead to far-red absorbance. Supporting Soulier’s hypothesis for how allophycocyanin might be modified, he showed that structural changes occur to flatten the red-light-absorbing chromophore that thereby enhance far-red-light absorbance. The next step in Soulier’s research will be to characterize how some cyanobacteria are able to grow in low-light conditions using a similar allophycocyanin absorbing far-red light.


Identifying the mechanisms by which cyanobacteria harvest light remains as a significant barrier to engineering stable far-red fluorophores. Understanding how cyanobacteria alter their physiology to adapt in different light conditions is important for improving their growth in photobioreactors. Better understanding of how these adaptations occur can also be utilized to manipulate plants genetically for more efficient light utilization. Finally, phycobiliprotein-based fluorophores, such as smURFP, can be used in the biological imaging of mammalian tissues. Identifying far-red fluorophores that can respond to even longer, and more penetrating, wavelengths of light could lead to substantial improvements in this process.  Soulier’s work has since been published in SpringerLink.

BMB is proud to have students like Soulier and congratulates him on both of his Honorable Mention awards as well as all his overall scientific success.


About Dr. Richard L. McCarl:

Richard L. McCarl earned his Ph.D. in Agricultural and Biological Chemistry from Penn State University in 1961. He was asked to stay at Penn State, where he served with distinction as a faculty member of the Department of Biochemistry, earning the respect of students and colleagues for his standards, dedication and concern for the students' growth under his watchful eyes. He had the unique ability to listen and reassure, followed by a nudge forward through thoughtful suggestions, but completed with action when necessary.

Dr. McCarl 's research interest included lipid and carbohydrate metabolism in cell and tissue cultures. In 1982, he made the transition to administration, serving a variety of roles in the Graduate School including Associate Dean of the Graduate School and Director of the Intercollege Research Program until his retirement in 1991.  He received the 2005 Eberly College of Science Distinguished Service Award.  During his tenure at Penn State, he was in charge of the Biochemistry Department's Small Animal Facilities, served on the Faculty Advisory Committee to the University President, was a member of the Task Force for Recruiting and Retention of Minority Graduate Students, and was a member of the Faculty Senate, serving on numerous committees.