[6] Following his post-doctoral research, Johnson began his academic career in 1984 as an Assistant Instructor of Microbiology and Molecular Genetics at Harvard Medical School.
[8] Johnson's research in toxicology has revealed insights into the properties, uses, and administration of botulinum toxin and other microbial neurotoxins in medicine, highlighting their implications.
More specifically, he contributed to the purification and standardization of botulinum toxin preparations, as well as determined critical manufacturing and testing steps for FDA approval in initial strabismus studies.
[10] Additionally, he explored different immunotypes of botulinum toxin, aiming to increase specific activity to reduce antigen exposure and prevent immunoresistance in human therapy.
He made contributions by serving on a team that identified SV2 as the protein receptor for botulinum neurotoxin A, demonstrating its binding mechanism and the impact of SV2 expression on toxin entry.
[11] Furthermore, he highlighted advancements in botulinum treatment systems, explored new indication areas, addressed challenges in therapy, and emphasized the importance of drug development projects and enhanced accessibility.
In 2001, he examined the production of neurotoxin (BoNT) by Clostridium botulinum, shedding light on the regulatory factors involved in neurotoxigenic clostridia.
Studying Clostridium botulinum strains Hall A, Okra B, and Iwanai E, he identified minimal nutritional requirements, advancing our understanding of essential nutrients and defined media for specific serotypes.