Jeffrey G. Johnson

Presented by Sidney Strickland on behalf of Tom Muir

B.A., Knox College

Studies on the Maturation of Secreted Quorum Sensing Peptides That Regulate S. aureus Virulence

Jeffrey Johnson received his undergraduate degree in chemistry from Knox College in Illinois before joining the Tri-Institutional Program in Chemical Biology in the fall of 2009. For his thesis work, Jeff studied how virulence is regulated in pathogenic staph bacteria through something called quorum sensing. For the non-specialists, staph in many ways act like soccer hooligans. When they are on their own they are relatively docile and harmless, but get them in a crowd, particularly in the presence of a chemical stimulant, and you’d better watch out. Indeed, staph turn on their virulence response (the ability of the infection to spread) only when their numbers have reached a certain threshold, hence the term quorum sensing—they use chemistry to count how many of their buddies are nearby before undergoing this Jekyll and Hyde transformation. During his time in my lab, Jeff focused on the biosynthesis and secretion mechanisms of the peptide-based “words” that bugs use to talk to each other. Using a combination of chemical and genetic tools, Jeff was able to make incisive contributions to our understanding of the multiple-step process that releases a cyclic peptide pheromone from the middle of a ribosomal polypeptide precursor. As part of this work, he developed an ingenious genetic method that allowed him to manufacture the mature peptide pheromone in staph in a manner that was totally orthogonal to the normal biosynthetic pathway and that, as a consequence, unveiled novel aspects of the secretion pathway. Indeed, Jeff’s insights have unleashed a whole new area of research in my lab related to peptide secretion and how this might be harnessed for the purposes of the development of novel therapeutic modalities.

In addition to his contributions at the bench, Jeff acted as a key social hub in the lab. He grew up pretty close to Las Vegas, and this clearly had an impact on his tastes in recreation. For instance, barely a sporting event went by without Jeff eagerly organizing a laboratory gambling pool. His honest and warm demeanor naturally drew people into these schemes. For my part, I never really understood how any of these worked since I consistently lost even when I picked the winner. Still, I will really miss listening to Jeff trying to explain the nuances of the bracket system (or was it racket system?) and will alas now have to find new ways of giving my money to the group. Jeff, I will really miss you in the lab, but I know that it is a good “bet” that you will go on great success in your future as a science journalist.