Quantitative Proteomics Combined with Phosphoproteome Reveals the Mechanism of the Density-Sensing Regulator QseC in the Pathogenesis of Glaesserella parasuis

QseC
is a sensor component of the two-component system
(TCS) QseBC
in Glaesserella parasuis (G. parasuis). Quantitative proteomics identifies
39 differentially expressed proteins (DEPs) (12 upregulated, 27 downregulated)
in ΔqseC, with the lipid metabolism enzyme
PlsB emerging as a core hub showing concurrent upregulation in total
protein expression and phosphorylation. Phosphoproteomics detects
95 phosphorylation sites, demonstrating predominant serine phosphorylation
(40%) and significant PlsB/SerS hyperphosphorylation. Functional analyses
show that deleting the qseC gene disrupts cellular balance. This change
causes an energy crisis involving ATPase imbalance and carbohydrate
metabolism defects. It also weakens the cell membrane by reducing
key lipopolysaccharide (LPS) biosynthesis proteins like LpxB, KdsB,
and WaaQ. Additionally, iron uptake becomes impaired because genes
such as hemG and fbpC2 are suppressed, along with defense proteins
HsdR and ApxIB. Finally, cells adopt an “offensive-defensive
shift” survival strategy. They do this by reducing energy-intensive
defenses like UvrA-mediated DNA repair and β-lactam resistance,
while increasing lipid storage (PlsB) and RNA degradation. Protein–protein
interaction (PPI) networks confirm 10 core proteins that collectively
maintain proteostasis and stress adaptation, with PlsB serving as
the central coordinator of membrane synthesis and environmental adaptation.

QseC是副猪嗜血杆菌（Glaesserella parasuis, G. parasuis）中双组分系统（two-component system, TCS）QseBC的感应组分。本研究通过定量蛋白质组学鉴定出ΔqseC突变株中存在39种差异表达蛋白（differentially expressed proteins, DEPs），其中12种蛋白表达上调、27种下调，脂代谢酶PlsB作为核心枢纽蛋白，在总蛋白表达与磷酸化水平上均呈现同步上调趋势。磷酸化蛋白质组学检测到95个磷酸化位点，结果显示丝氨酸磷酸化占主导比例（40%），且PlsB/SerS出现显著的过度磷酸化。功能分析表明，敲除qseC基因会破坏细胞稳态，该变化引发以ATP酶失衡、碳水化合物代谢缺陷为特征的能量危机；同时通过下调LpxB、KdsB、WaaQ等关键脂多糖（lipopolysaccharide, LPS）生物合成蛋白的表达，削弱细胞膜完整性。此外，hemG、fbpC2等基因以及防御蛋白HsdR与ApxIB的表达被抑制，导致细胞铁摄取能力受损。最终，细胞采取“攻防转换”的生存策略：下调UvrA介导的DNA修复、β-内酰胺类耐药等高能耗防御机制，同时上调脂质储存（PlsB）与RNA降解过程。蛋白质相互作用（protein–protein interaction, PPI）网络验证了10种核心蛋白，它们协同维持蛋白质稳态与应激适应，其中PlsB作为膜合成与环境适应的核心协调者发挥关键作用。