Biology subjects

Norris, S. J.

Publications and source records attributed to Norris, S. J..

4 recordsLinked to original sources

bioRxiv2026

Human placental trophoblasts support sustained Treponema pallidum replication and reveal new candidate host pathways implicated in congenital syphilis

Congenital syphilis is a leading cause of preventable stillbirth, yet the mechanisms that enable Treponema pallidum subsp. pallidum, the etiological agent of syphilis, to traverse and persist within the human placenta are virtually unknown. This knowledge gap reflects, in part, the fastidious nature of T. pallidum, which has historically only been propagated in rabbit epithelial cells. Here, we demonstrate that T. pallidum replicates and can be propagated long-term in human placental trophoblast models. We identified three human trophoblast cell lines, JEG-3, BeWo, and HTR-8, that sustained robust T. pallidum replication for over 55 days. Confocal imaging with GFP-expressing T. pallidum demonstrated bacterial adherence to trophoblast cultures. To identify human placental pathways that may support T. pallidum replication and persistence, we performed bulk transcriptomic profiling of the three trophoblast lines co-cultured with T. pallidum for 3 or 7 days. Our findings revealed conserved host responses involving increased cholesterol synthesis, suppressed type I interferon signaling, and disrupted extracellular matrix organization. These data implicate host metabolic rewiring, innate immune attenuation, and extracellular matrix remodeling as candidate pathways that may promote T. pallidum invasion, replication and persistence within the placenta. Together, these models represent the first human placental systems capable of supporting efficient, long-term T. pallidum growth and provide a foundation for mechanistic studies of congenital syphilis pathogenesis.

microbiology↗

bioRxiv2020

Molecular Mechanism for Rotational Switching of the Bacterial Flagellar Motor

The bacterial flagellar motor is a remarkable nanomachine that can rapidly rotate in both counter-clockwise (CCW) and clockwise (CW) senses. The transitions between CCW and CW rotation are critical for chemotaxis, and they are controlled by a signaling protein (CheY-P) that interacts with a switch complex at the cytoplasmic side of the flagellar motor. However, the exact molecular mechanism by which CheY-P controls the motor rotational switch remains enigmatic. Here, we use the Lyme disease spirochete, Borrelia burgdorferi, as the model system to dissect the mechanism underlying flagellar rotational switching. We first determined high resolution in situ motor structures in the cheX and cheY3 mutants in which motors are genetically locked in CCW or CW rotation. The structures showed that the CheY3 protein of B. burgdorferi interacts directly with the FliM protein of the switch complex in a phosphorylation-dependent manner. The binding of CheY3-P to FliM induces a major remodeling of the switch protein FliG2 that alters its interaction with the torque generator. Because the remodeling of FliG2 is directly correlated with the rotational direction, our data lead to a model for flagellar function in which the torque generator rotates in response to an inward flow of H+ driven by the proton motive force. Rapid conformational changes of FliG2 allow the switch complex to interact with opposite sides of the rotating torque generator, thereby facilitating rotational switching between CW and CCW.

microbiology↗

bioRxiv2019

In situ structures of periplasmic flagella in Borrelia reveals conformational changes essential for flagellar rotation

The bacterial flagellar motor is a molecular machine that rotates the flagellar filament at high speed. Torque is generated by the stator-rotor interaction coupled to an ion flux through the torque-generating stator. Here, we employed cryo-electron tomography to visualize the intact flagellar motor in the Lyme disease spirochete Borrelia burgdorferi. By analysis of the motor structures of wild-type and stator mutants, we localize the torque-generating units precisely and determine three-dimensional structure of the stator and its interactions with the rotor. Our study shows that the cytoplasmic domains of the stator are packed regularly around the circumference of the flagellar C-ring. The stator-rotor interaction induces a profound conformational change in the C-ring. Analysis of the motors of a less motile motB-D24E mutant and a non-motile motB-D24N mutant, in which the proton translocation is reduced and blocked, respectively, provides evidence that the conformational change of the C-ring is essential for flagellar rotation.

microbiology↗

bioRxiv2018

In situ structures of periplasmic flagella reveal a distinct cytoplasmic ATPase complex in Borrelia burgdorferi

Periplasmic flagella are essential for the distinct morphology and motility of spirochetes. A flagella-specific Type III secretion system (fT3SS) composed of a membrane-bound export apparatus and a cytosolic ATPase complex is responsible for the assembly of the periplasmic flagella. Here, we combine cryo-electron tomography and mutagenesis approaches to characterize the fT3SS machine in the Lyme disease spirochete Borrelia burgdorferi. We define the fT3SS machine by systematically characterizing mutants lacking key component genes. We discover that a distinct cytosolic ATPase complex is attached to the flagellar C-ring through multiple spoke-like linkers. The ATPase complex not only strengthens structural rigidity of the C-ring, but also undergoes conformational changes in concert with flagellar rotation. Our studies provide structural framework to uncover the unique mechanisms underlying assembly and rotation of the periplasmic flagella and may provide the bases for the development of novel therapeutic strategies against several pathogenic spirochetes.

microbiology↗