Proteolysis of <scp>BB</scp>0323 results in two polypeptides that impact physiologic and infectious phenotypes in <i><scp>B</scp>orrelia burgdorferi</i>

<jats:title>Summary</jats:title><jats:p><jats:italic><jats:styled-content style="fixed-case">B</jats:styled-content>orrelia burgdorferi</jats:italic> gene product <jats:styled-content style="fixed-case">BB</jats:styled-content>0323 is required for cell fission and pathogen persistence <jats:italic>in vivo</jats:italic>. Here, we show that <jats:styled-content style="fixed-case">BB</jats:styled-content>0323, which is conserved among globally prevalent infectious strains, supports normal spirochaete growth and morphology even at early phases of cell division. We demonstrate that native <jats:styled-content style="fixed-case">BB</jats:styled-content>0323 undergoes proteolytic processing at the <jats:styled-content style="fixed-case">C</jats:styled-content>‐terminus, at a site after the first 202 <jats:styled-content style="fixed-case">N</jats:styled-content>‐terminal amino acids. We further identified a periplasmic <jats:styled-content style="fixed-case">BB</jats:styled-content>0323 binding protein in <jats:italic><jats:styled-content style="fixed-case">B</jats:styled-content>. burgdorferi</jats:italic>, annotated as <jats:styled-content style="fixed-case">BB</jats:styled-content>0104, having serine protease activity responsible for the primary cleavage of <jats:styled-content style="fixed-case">BB</jats:styled-content>0323 to produce discrete <jats:styled-content style="fixed-case">N</jats:styled-content>‐ and <jats:styled-content style="fixed-case">C</jats:styled-content>‐terminal polypeptides. These two <jats:styled-content style="fixed-case">BB</jats:styled-content>0323 polypeptides interact with each other, and either individually or as a complex, are associated with multiple functions in spirochaete biology and infectivity. While <jats:styled-content style="fixed-case">N</jats:styled-content>‐terminal <jats:styled-content style="fixed-case">BB</jats:styled-content>0323 is adequate to support cell fission, the <jats:styled-content style="fixed-case">C</jats:styled-content>‐terminal <jats:styled-content style="fixed-case">LysM</jats:styled-content> domain is dispensable for this process, despite its ability to bind <jats:italic><jats:styled-content style="fixed-case">B</jats:styled-content>. burgdorferi</jats:italic> peptidoglycan. However, the <jats:styled-content style="fixed-case">LysM</jats:styled-content> domain or the precisely processed <jats:styled-content style="fixed-case">BB</jats:styled-content>0323 product is essential for mammalian infection. As <jats:styled-content style="fixed-case">BB</jats:styled-content>0323 is a membrane protein crucial for <jats:italic><jats:styled-content style="fixed-case">B</jats:styled-content>. burgdorferi</jats:italic> survival <jats:italic>in vivo</jats:italic>, exploring its function may suggest novel ways to interrupt infection while enhancing our understanding of the intricate spirochaete fission process.</jats:p>