An Interaction between the Inner Rod Protein YscI and the Needle Protein YscF Is Required to Assemble the Needle Structure of the Yersinia Type Three Secretion System.

The type III secretion system is a highly conserved virulence mechanism that is widely distributed in Gram-negative bacteria. It has a syringe-like structure composed of a multi-ring basal body that spans the bacterial envelope and a projecting needle that delivers virulence effectors into host cells. Here, we showed that the Yersinia inner rod protein YscI directly interacts with the needle protein YscF inside the bacterial cells and that this interaction depends on amino acid residues 83-102 in the carboxyl terminus of YscI. Alanine substitution of Trp-85 or Ser-86 abrogated the binding of YscI to YscF as well as needle assembly and the secretion of effectors (Yops) and the needle tip protein LcrV. However, yscI null mutants that were trans-complemented with YscI mutants that bind YscF still assembled the needle and secreted Yops, demonstrating that a direct interaction between YscF and YscI is critical for these processes. Consistently, YscI mutants that did not bind YscF resulted in greatly decreased HeLa cell cytotoxicity. Together, these results show that YscI participates in needle assembly by directly interacting with YscF.

[Effects of praeruptorin C on cell hypertrophy, intracellular [Ca2+]i, nitric oxide and signal transduction in isolated hypertrophied rat smooth muscle cells induced by angiotensin II].

AIM: To investigate the effects of praeruptorin C (Pra-C) on smooth muscle cell (SMC) hypertrophy, intracellular calcium ([Ca2+]i), nitric oxide (NO) content and influence on cellular signal transduction in isolated cultured rat smooth muscle cell (SMC). METHODS: Hypertrophied smooth muscle cells (HSMCs) were induced by angiotensin II (Ang II), cell area was measured under inverted microscope. Nitric oxide (NO) concentration was measured using Griess method. [Ca2+]i was measured using Fura-2/AM. The responses to [Ca2+]i elevation stimulated by KCl (60 mmol.L-1 or norepinephrine (10 mumol.L-1) were observed by incubation with phorbol 12-myristate 13-acetate (PMA), staurosporine (ST), the agonist and inhibitor of protein kinase C (PKC), and pertussis toxin (PTX), the sensitive toxin of Gi. RESULTS: The cell area of SMCs were decreased by 39.01% (P < 0.001) and NO content of SMCs were significantly increased in Pra-C + Ang II group. In presence of 60 mmol.L-1 KCl or 10 mumol.L-1 NE, [Ca2+]i of SMCs in Pra-C + Ang II group was significantly decreased than that of Ang II group (P < 0.001) and closed to the normal group. Incubation of SMCs with PMA, ST and PTX, [Ca2+]i of SMCs in Ang II group was increased by PMA and decreased by ST and PTX, but that of Pra-C + Ang II group was similar to the normal group. CONCLUSION: These findings suggest that Pra-C can reduce vascular hypertrophy in isolated rat HSMCs, and this is associated with improvement of SMCs [Ca2+]i level, NO content and cellular signal transdution of PKC and Gi.