Biology subjects

Panjalingam, M.

Publications and source records attributed to Panjalingam, M..

3 recordsLinked to original sources

bioRxiv2025

Twin-arginine transport complex plays an essential role in Caulobacter cell shape and viability

Two main pathways are responsible for protein secretion across the cytoplasmic membrane in prokaryotes. While the general secretory (Sec) pathway transports proteins across the membrane in an unfolded state, the twin-arginine translocation (Tat) pathway transports proteins primarily in their folded conformation. Although the Tat system appears dispensable in multiple model bacteria, some species require it for viability, and the reason for the distinction is nebulous. Here we show that all three subunits of the Tat complex -- TatA, TatB, and TatC -- are essential in the alpha-proteobacterium Caulobacter crescentus. Additionally, depletion of the Tat complex results in abnormal cell morphology. We found that localization to the cell periphery, as well as midcell localization upon osmotic upshift, of the essential peptidoglycan transpeptidase PBP2 is dependent on the Tat apparatus. In contrast, subcellular localization of the actin homolog MreB and the penicillin-binding protein PBP1a is not perturbed upon depletion of the Tat complex. PBP2 transpeptidase activity links glycan chains at sites of cell wall remodeling and is essential for cell elongation. Together these results suggest that PBP2 localization is a key responsibility of the Tat system in Caulobacter and possibly other alpha-proteobacteria. Significance StatementO_LIThe twin-arginine translocation (Tat) system is essential for viability in some bacteria but not others. The essential role that the Tat pathway plays in these bacteria is not well understood. C_LIO_LIThe Tat complex is essential in Caulobacter crescentus and required for the cell wall synthesis protein PBP2 to localize to the cell envelope. C_LIO_LIPBP2 is critical for viability and maintenance of cell shape in Caulobacter, and essentiality of the Tat complex may be partly attributed to its role in localizing PBP2. C_LI

microbiology↗

bioRxiv2023

The Biogenesis of Bacterial PHB Granules

PHB granules are bacterial organelles that store excess carbohydrates in the form of water-insoluble polyhydroxybutyrate (PHB). The PHB polymerase, phasin (a small amphipathic protein), and active PHB synthesis are essential for the formation of mature PHB granules in Caulobacter crescentus. Granule formation was found to be initiated by the condensation of self-associating PHB polymerase-GFP into foci, closely followed by the recruitment and condensation of phasin-mCherry. Following the active synthesis of PHB and granule maturation, the polymerase dissociates from mature granules and the PHB depolymerase is recruited to the granule. The polymerase directly binds phasin in vitro through its intrinsically disordered N-terminal domain. Thus, granule biogenesis is initiated and controlled by the action of a PHB polymerase and an associated helper protein, phasin, that together synthesize the hydrophobic granule content while forming the granules protein boundary. ImportanceLike eukaryotes, bacteria organize their cytoplasm in subcellular compartments. These bacterial compartments can be membrane-bound (e.g. magnetosomes), or membraneless with protein-encased shells (e.g. carboxysomes). Here we investigate how Caulobacter forms membrane-less compartments that store the water-insoluble carbohydrate polymer polyhydroxybutyrate (PHB). A PHB polymerase is essential for granule biogenesis and we observed a direct interaction with the granule associated protein phasin through the disordered N-terminus of the polymerase. We found that PHB granules form by sequential recruitment of key proteins, beginning with the polymerase, and that the granule composition changes as these organelles mature.

molecular biology↗

bioRxiv2023

Phosphatase to kinase switch of a critical enzyme contributes to timing of cell differentiation

Cell differentiation is an essential biological process that is often subject to strict temporal regulation. The aquatic bacterium, Caulobacter crescentus, undergoes obligate differentiation from a swarmer cell to a stationary, replication-competent stalked cell, with each cell cycle. Here, we report that the switch from phosphatase to kinase activity of the histidine kinase PleC contributes to timing this differentiation event. We show that PleC PAS domain interaction with the polar scaffold protein PodJ localizes PleC to the cell pole and inhibits in vivo kinase activity. Upon PodJ degradation, released PleC switches to its kinase form and phosphorylates the PleD diguanylate cyclase, initiating the signaling pathway responsible for differentiation. While PodJ inhibits PleC kinase activity, it does not impact PleC phosphatase activity on DivK, which is required for pili biogenesis and flagellar rotation. Thus, PleC PAS domain interaction with PodJ regulates PleC subcellular localization, enzymatic activity, and the timing of cell differentiation, revealing that PAS domains affect enzymatic function on diverse substrates by relying on context dependent binding partners.

developmental biology↗