Kevin D. Young, Ph.D.Department Chair

Professor, Department of Microbiology & Immunology 

Research Interest: Genetics and physiology of E. coli cell division and bacterial cell shape
Ph.D., University of Oklahoma
Postdoctoral:  Texas A&M University, University of California at Berkeley
Phone: (501) 526-6802
Fax:  (501) 686-5359

E-mail

Research Description

Peptidoglycan is unique to the eubacteria and is the rigid macromolecule that defines their shape, protects them from osmotic shock and lysis, and which can behave as a trans-acting signal or toxin towards eukaryotic cells. The long-term goal of my laboratory is to explain the structure, synthesis, and remodeling of bacterial peptidoglycan, with the aim of understanding its contribution to fundamental prokaryotic cell biology, bacterial pathogenesis and immunoregulation. In particular, we are addressing the following questions: What are the proteins, substrates, and products involved in the construction and maintenance of peptidoglycan? How might these processes be regulated? In what way does peptidoglycan composition and structure affect bacterial physiology? How is cell shape determined? And how does the cell determine whether to make lateral wall or a division septum?

Penicillin and its relatives, the beta-lactam antibiotics, kill bacteria by inactivating penicillin-binding proteins (PBPs), a set of enzymes responsible for the latter stages of peptidoglycan synthesis and maintenance. In Escherichia coli, the identity of seven PBPs has been known for three decades. Nevertheless, we know very little about how these proteins contribute to the physiology of a bacterial cell and cannot describe in detail the pathways by which PBPs assemble and remodel mature peptidoglycan. Although we have a wealth of biochemical data about how a few PBPs operate in isolation, this knowledge does not necessarily reflect or explain the in vivo roles of each PBP. In addition, the PBPs may have functions we do not yet know how to measure. For the most part, our in vivo knowledge of what PBPs do for the cell is based on defects that accompany mutation or inactivation of individual PBPs. However, several PBPs share common enzymatic activities so the phenotypes that accompany the loss of one protein may be masked by the action of another. Thus, in practice, the absence of most individual PBPs produces no identifiable phenotype. The end result is that we cannot answer some very basic questions about how the cell wall is built or how it contributes to the physiology of the cell envelope.

We have addressed this problem by systematically mutating PBP genes in multiple combinations to visualize new phenotypes. From a comprehensive set of over 400 multiple-deletion mutants, we found unanticipated phenotypes and previously unknown physiological roles for the PBPs and peptidoglycan. The principle effect of removing PBPs is that certain mutants cannot maintain wild type diameter or shape. The most visually dramatic discovery is of a heretofore unknown relationship between the single domain PBPs and FtsZ, the major regulator of bacterial cell division. For example, some mutants interact with a missense FtsZ protein to grow in tight spirals instead of as straight rods. In pursuing the mechanisms behind these findings, we also found that the outer membrane and proteins embedded within it are organized in a helical fashion, with implications for the synthesis of all layers of the Gram negative bacterial envelope. Finally, the practical importance of these “nonessential” PBPs appears to be much greater than supposed. Several organisms elaborate peptidoglycan-based toxins, and other wall fragments are recognized specifically by a set of peptidoglycan binding proteins (PGRPs) comprising part of the innate immune response in eukaryotes. These circumstances argue that many of the PBPs may be involved in modifying peptidoglycan to create virulence factors or to elude and manipulate host immunity. Also of practical interest are potential applications of harnessing these enzymes to construct nanometer-sized vessels of defined shapes and dimensions. In summary, understanding peptidoglycan biology has become more imperative than ever, and our mutants are a particularly valuable resource with which to approach these new problems and applications.

References

Dev K. Ranjit, Matthew A. Jorgenson and Kevin D. Young.  2017.  PBP1B glycosyltransferase and transpeptidase activities play different essential roles during the de novo regeneration of rod-shaped morphology in Escherichia coli. J. Bacteriol. 199:e00612-16.

Matthew A. Jorgenson and Kevin D. Young.  2016.  Interrupting biosynthesis of O antigen or the lipopolysaccharide core produces morphological defects in Escherichia coli by sequestering undecaprenyl phosphate. J. Bacteriol. 198:3070-3079.

Katharina Peters, Suresh Kannan, Vincenzo A. Rao, Jacob Biboy, Daniela Vollmer, Stephen W. Erickson, Richard J. Lewis, Kevin D. Young, Waldemar Vollmer.  2016.  The redundancy of peptidoglycan carboxypeptidases ensures robust cell shape maintenance in Escherichia coli mBio 2016, 7.

Dev K. Ranjit and Kevin D. Young.  2016.  Colanic acid intermediates prevent de novo shape recovery of Escherichia coli spheroplasts, calling into question biological roles previously attributed to colanic acid.  J. Bacteriol. 193:1230-1240.

Matthew A. Jorgenson, Suresh Kannan, Mary E. Laubacher and Kevin D. Young.  2016.  Dead-end intermediates in the enterobacterial common antigen pathway induce morphological defects in Escherichia coli by competing for undecaprenyl phosphate.  Molecular Microbiology 100:1-14.

Li, Gang and Kevin D. Young.  2015.  A new suite of tnaA mutants suggests that Escherichia coli tryptophanase is regulated by intracellular sequestration and by occlusion of its active site. BMC Microbiology 15:14.  doi:10.1186/s12866-015-0346-3

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