Shoichi Tachiyama

Many gram-negative bacteria develop large protein complexes on their bacterial membranes that contribute to pathogenesis. The type III secretion system (T3SS), also called injectisome, and flagella are large protein complexes on bacterial membranes. Shigella develops and uses T3SS to directly translocate bacterial proteins into eukaryotic cells to change host cell functions, thereby reaping bacterial benefits by impacting immune system responses and bacterial motility within hosts. Although T3SS is essential to Shigella pathogenesis, the structural details and functions of each protein are not clearly understood. Previously, cryo-ET revealed an architecture on the cytoplasmic side of Shigella T3SS on minicells resulting from abnormal cell divisions. This location, called the cytoplasmic sorting platform, is an important protein complex to select and translocate bacterial proteins into host cells. Our laboratory has focused on structural details of the sorting platform to understand how bacterial proteins are injected into eukaryotic cells. To understand molecular functions of proteins in the sorting platform, our laboratory has collaborated with Dr. William Picking, University of Kansas. In our additional investigations of the flagella system, we also collaborate with Dr. Timothy Hoover, University of Georgia. We focus on architectures of flagella in Helicobacter pylori, a pathogen that uses flagella to localize in the human stomach to cause gastritis and peptic ulcer. This work aims to elucidate how H. pylori regulates flagella assembly. Our laboratory uses cryo-ET to observe the architecture of flagella structures on both bacterial membranes, termed the motor, which contribute to bacterial motility.