Allaoui, 1993 (Characterization of the Shigella flexneri ipgD and ipgF genes, which are located in the proximal part of the mxi locus.) [Article]

Q: What is the predicted size and structure of the IpgD protein?

A: "The ipgD gene is predicted to encode a 538-amino-acid-residue polypeptide with a calculated Mr of 59,764."

Q: What was observed regarding IpgD secretion in wild-type vs mutant strains?

A: "Comparison of the protein contents in the culture supernatants of the wild-type and ipgD strains indicated that the protein of 58 kDa was missing in the culture supernatant of the ipgD mutant"

Q: How is ipgD expression regulated by temperature?

A: "β-Galactosidase activity was 30-fold higher after growth of SF134 at 37°C than at 30°C (640 U versus 25 U), confirming that expression of ipgD, like the invasive phenotype of S. flexneri, is regulated by temperature."

Q: What is the genetic organization of ipgD and surrounding genes?

A: "There are 9 bp between the ipgD stop codon and the ipgE start codon and a 1-bp overlap between the ipgE stop codon and the ipgF start codon. This organization suggests that ipgD, ipgE, and ipgF belong to the same transcriptional unit."

Q: What was the effect of ipgD mutation on Shigella virulence?

A: "The ipgD mutant showed the same ability as the wild-type strain to invade HeLa cells, to induce the formation of plaques on confluent monolayers of HeLa cells, and to provoke keratoconjunctivitis in guinea pigs."

Q: How was secretion of IpgD protein confirmed in complementation studies?

A: "Secretion of the 58-kDa protein was restored in the ipgD mutant harboring plasmid pAB17"

Q: What is surprising about IpgD's role in relation to virulence?

A: "It thus appears that two secreted proteins, IpaA and possibly IpgD, are not involved in the virulent phenotype of S. flexneri. This is very surprising, especially considering the positions of the ipaA and ipgD genes in the invasion region of the virulence plasmid and the presence of the encoded proteins among the few proteins that are secreted into the culture supernatant."