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Previously, the authors have shown that inactivation of Shigella flexneri yihE, a gene of unknown function upstream of dsbA, which encodes a periplasmic disulphide catalyst, results in a global change of gene expression. Among the severely down-regulated genes are galETKM, suggesting that the yihE mutant, Sh54, may inefficiently produce the UDP-glucose and UDP-galactose required for LPS synthesis. This paper demonstrates that LPS synthesis in Sh54 is impaired. As a result, Sh54 is unable to polymerize host cell actin, due to aberrant localization of IcsA, or to cause keratoconjunctivitis in guinea pigs. Furthermore, Sh54 is more sensitive to some antimicrobial agents, and exhibits epithelial cytotoxicity characteristic of neither wild-type nor dsbA mutants. Supplying galETK in trans restores LPS synthesis and corrects all the defects. Hence, it is clear that the Shigella yihE gene is important not only in regulating global gene expression, as shown previously, but also in virulence through LPS synthesis via regulating the expression of the galETK operon.

Immediately prior to invasion Toxoplasma gondii tachyzoites release a large number of micronemal proteins (TgMICs) that participate in host cell attachment and penetration. The TgMIC4-MIC1-MIC6 complex was the first to be identified in T. gondii and has been recently shown to be critical in invasion. This study establishes that the N-terminal throm- bospondin type I repeat-like domains (TSR1-like) from TgMIC1 function as an independent adhesin as well as promoting association with TgMIC4. Using the newly solved three-dimensional structure of the C-terminal domain of TgMIC1 we have identified a novel Galectin-like fold that does not possess carbohydrate binding properties and redefines the architecture of TgMIC1. Instead, the TgMIC1 Galectin-like domain interacts and stabilizes TgMIC6, which provides the basis for a highly specific quality control mechanism for successful exit from the early secretory compartments and for subsequent trafficking of the complex to the micronemes. [ABSTRACT FROM AUTHOR]

Examines the complete resonance assignments of the C-terminal domain from the micronemal protein (MIC1) of the protozoan parasite, Toxoplasma gondii. Nature of the interaction between MIC1 and host cells; Role of MIC1 in the parasite's invasion of the human body that can eventually result to toxoplasmosis.